Regenerated engine with an improved heating stroke

ABSTRACT

An improved, reciprocating internal combustion engine is disclosed herein. This engine consists of multiple cylinders, each closed by a cylinder head and containing a piston which is connected to a power output shaft. Each cylinder has means for the intake and exhaust of working fluid. It also contains a movable, thermal regenerator, an alternating flow heat exchanger, and means to move this regenerator. Finally, means are provided for the introduction of fuel into the cylinder. The regenerated, internal combustion, reciprocating engine and several variations on it disclosed herein are substantially different from prior art and provide critical improvements over that prior art. These improvements include different operating processes--especially an improved heating stroke, the use of unequal effective compression and expansion ratios, non direct fuel injection, and others.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to thermally regenerated, reciprocating, internalcombustion engines that employ a movable regenerator.

2. Description of the Related Art

Thermal regeneration is the capturing of waste heat from a thermodynamiccycle (or a heat engine operating on some thermodynamic cycle), and theutilization of that energy within the cycle or engine to improve thecycle or engine's performance. This is commonly done with many heatengines, including Stirling engines, gas turbines, and Rankine cycledevices. In a gas turbine, consisting of a compressor, combustor, andturbine, the temperature of the air leaving the turbine is often greaterthan the temperature of the air leaving the compressor. If the energy inthe turbines exhaust can be transferred to the air leaving thecompressor, it will not be necessary to add as much heat (fuel) in thecombustor to raise the air temperature to the desired turbine inlettemperature. This means that the same work is accomplished, but lessfuel is employed. Therefore, the specific fuel consumption of such athermally regenerated gas turbine is improved. Thermal regeneration ofgas turbines is commonly accomplished by the use of a heat exchangerthat transfers energy from the exhaust gases to the compressed air.

Gasoline and diesel engine operation is generally approximated by athermodynamic cycle referred to as the Otto cycle. In principle, an Ottocycle can also be thermally regenerated. This would be done bytransferring heat from the gases at the conclusion of the expansionstroke to the gases of the next cycle at the conclusion of thecompression stroke. The benefits that can be thus attained aresubstantial. Fuel consumption is reduced in a manner similar to that ofthe regenerated gas turbine. In addition, a regenerated Otto cycle isthermodynamically capable of providing higher gas temperatures duringthe cycle, which results in even greater improvements in efficiency andpower. Since reciprocating engines only experience these highertemperatures for brief times, they can withstand these highertemperatures to some extent. Thus the benefits of regeneration are evengreater for an Otto cycle device than they are for the temperaturelimited gas turbine.

The advantages of thermally regenerated gasoline or diesel engines arereadily apparent and quite substantial. Unfortunately, viable andeffective means by which this can be accomplished have not previouslybeen developed. The difficulty lies in the fact that the compression,heating and expansion processes occur in the same location--i.e. withinthe cylinder. This makes it difficult to conceive of some means by whichthe heat can be captured and transferred to the compressed air at adifferent time in the cycle. For a gas turbine, which is a steady flowdevice with the cycle processes separated in space, it is relativelyeasy to add a heat exchanger at the appropriate place. It is much moredifficult to do this in a non-steady flow, reciprocating engine whereall the processes occur in the same location.

The approach taken by most inventors who attempted to incorporateregeneration into reciprocating internal combustion engines was toseparate the engine processes in space. In this way it becomesrelatively easy to insert a heat exchanger between the engine componentsthat accomplish each process. This has led to a number of approachessuch as those of Hirsch (1874, U.S. Pat. No. 155,087), Martinka (1937,U.S. Pat. No. 2,239,922), Pattas (1973, U.S. Pat. No. 3,777,718), Bland(1975, U.S. Pat. No. 3,871,179), Pfefferle (1975, U.S. Pat. No.3,923,011), Cowans (1977, U.S. Pat. No. 4,004,421), Stockton (1978, U.S.Pat. No. 4,074,533), Webber (1986, U.S. Pat. No. 4,630,447), Ruiz (SAEpaper 930063, 1993), and Carmichael (Chrjapin Master's thesis, MIT,1975). All of these approaches involve at least two cylinders, generallyone in which compression occurs and a second where the combustion andexpansion occur. In the flow passage connecting these cylinders or inone of the cylinders there is a stationary permeable material thatcomprises the regenerator. The regenerator is an alternating flow heatexchanger. The expanded combustion gases are passed through theregenerator and transfer thermal energy to it. During the next cyclecompressed air is forced through the regenerator and absorbs thisenergy. Thus heat is transferred from the hot exhaust gases to thecompressed air--the essence of thermal regeneration.

Unfortunately, none of these earlier approaches for regeneration ofinternal combustion reciprocation engines have been successful. Thereason for their failure lies in a basic feature of thoseapproaches--the separation of the processes into different cylinders.Because some air and exhaust is always trapped in the transfer passages,because of "blowdown" losses between cylinders in some designs, andbecause not all of the air can be regeneratively heated or cooled, or bein the appropriate locations at the optimum times, the performance ofthese engines is reduced.

More recently, a new approach has been conceived. This new approachallows the processes to occur within a single cylinder. The most uniquefeature of this new approach is a movable regenerator. This regeneratoris in the form of a thin disc with a diameter essentially equal to theengine bore. This regenerator disc is located between the cylinder headand the piston. This moving regenerator sweeps through all of theinternal volume of the cylinder twice during each engine operatingcycle. As it moves through the gas in the cylinder, it exchanges energywith that gas. One sweep removes energy from the expanded combustionproducts. The other sweep transfers this energy to the compressedworking fluid near the conclusion of the next compression stroke. Theregenerator movement that occurs near the end of the expansion strokeand cools the combustion products is referred to as the regenerativecooling stroke. The regenerator movement that starts near the end of thecompression stroke and heats the compressed air is referred to as theregenerative heating stroke. Inventions based upon this approach of amovable regenerator are included in the patents of Ferrenberg (1988,U.S. Pat. No. 4,790,284 and 1990, U.S. Pat. No. 4,928,658) and Millman(1981, U.S. Pat. No. 4,280,468).

Regenerated engines employing movable regenerators that sweep throughthe interior volume of the cylinder can be divided into two classes:those in which the combustion occurs between the piston and theregenerator (hot piston designs) and those in which the combustionoccurs between the regenerator and the cylinder head (cool or coldpiston designs). The "hot volume" is always the volume where thecombustion occurs and the "cold volume" lies on the other side of theregenerator. The side of the regenerator that faces the hot volume isreferred to as the hot side of the regenerator and the side of theregenerator that faces the cold volume is the cold side of theregenerator.

In addition to other regenerated engine inventions unrelated to thispatent application, Millman (U.S. Pat. No. 4,280,468) discloses andclaims a hot piston regenerated engine operating on a four stroke cycle.This engine of Millman's lacks a regenerative cooling stroke. Instead,he maintains the regenerator stationary and adjacent to the valves inthe cylinder head while the blowdown and the exhaust occur. This is aserious deficiency in the manner in which the energy is extracted fromthe working fluid by the regenerator that can substantially degradeengine performance. In addition, Millman does not consider the use ofdifferent compression to expansion ratios, cool piston regeneratedengines, two stroke regenerated engines, and regenerated enginesincorporating many of the other features and innovations disclosed inthis patent application.

The previous disclosures of Ferrenberg (U.S. Pat. Nos. 4,790,284 and4,928,658) cover both two and four stroke, and hot and cool pistonregenerated engines. However, these earlier inventions have some basicdeficiencies that are corrected by the substantially different operationof the regenerated engine disclosed herein. In addition, these earlierengines do not include the use of, or means for, differing compressionand expansion ratios, the introduction of fuel by means other thandirect injection into the combustion region, throttling as a means toreduce power and maintain high efficiency, the use of flush mountedvalves in cool piston engines, the use of regenerators made from ceramicfoam materials, pneumatic regenerator lifters, and other features andinnovations disclosed herein. In addition, these earlier patents ofFerrenberg maintain the regenerator stationary during the blowdown orfail to substantially complete the regenerative cooling stroke prior tothe blowdown. This is similar to the deficiency of Millman's engine.Also, the earlier disclosures and claims of Ferrenberg specificallyclose the exhaust valve prior to the opening of the intake valve in allregenerated engines employing valves. It is highly advantageous to haveboth valves open at the same time, for a short period.

Other substantial differences exist between the earlier inventions ofMillman and Ferrenberg, and the regenerated engine disclosed herein. Allof these are discussed in greater detail in the section entitled"Detailed Description of the Invention".

SUMMARY OF THE INVENTION

This invention is an internal combustion, reciprocating, regeneratedengine made up of a number of similar working units, often referred toas cylinders. Each working unit is comprised of a cylinder that isclosed at one end by a cylinder head and contains a movable piston thatis connected to a power output shaft. Means are provided to permit andcontrol the flow of working fluid into and out of the cylinder. Analternating flow heat exchanger, called a regenerator, is located withinthe cylinder, between the piston and the cylinder head. This regeneratorcan move between the piston and the cylinder head, and means areprovided to accomplish this movement at the appropriate times during theengine's operating cycle. This movement of the regenerator is such thatthe regenerative heating stroke begins during the last quarter of thepiston's compression stroke and ends during the first quarter of thepiston's expansion stroke. This movement is of such speed and timing soas to maintain, to the greatest extent possible, a flow of working fluidthrough the regenerator, from the regenerator's cold side to its hotside, throughout the regenerator's motion. Finally, means are providedfor the introduction of fuel into the cylinder during this regenerativeheating stroke.

One embodiment of this invention controls the intake means opening andclosing times so that the degree of compression which the working fluidexperiences in the cylinder is less than the degree of expansion. Otherembodiments provide fuel introduction means that provide for fuelintroduction (1) on the cold side of the regenerator and (2) with theincoming fresh working fluid. Additional embodiments include intake andexhaust means that include the flow of a portion of the working fluidthrough a tube or other means used to move the regenerator. Anotherembodiment provides means for reducing the amount of working fluid thatenters the cylinder. Additional embodiments that are applicable to coolpiston regenerated engines provide intake and exhaust means that arelocated in the cylinder wall and are substantially flush mounted in thatcylinder wall when closed. One further embodiment that is onlyapplicable to regenerated engines with valves provides for valves thatare so operable that both the intake and the exhaust valves may be openat the same time during the operating cycle.

Additional embodiments of this invention provide for catalytic materialson the regenerator's surfaces that (1) increase the reactivity of thefresh working fluid passing through it or (2) reduce pollutants in thespent working fluid passing through it.

Another embodiment of this invention provides a regenerator havinginternal flow passages that are of different average size in differentportions of the regenerator.

An additional embodiment of this invention employs a secondary pistonconnected to the regenerator which is acted upon by the pressure in thecylinder so as to provide a portion of the force required to place theregenerator at the appropriate locations at the appropriate times in theoperating cycle.

A final embodiment of this invention provides means for moving theregenerator that include means for providing variations in the cyclicmotion of the regenerator as a function of the engine's speed and load.

OBJECTS OF THE INVENTION

The primary object of this invention is to provide a highly efficient,regenerated, internal combustion engine.

Another object of this invention is to provide an engine with very highbrake mean effective pressure.

Another object of this invention is to provide a regenerator that cansurvive and function in the engine environment.

Another object of this invention is to exploit the high payoff to beobtained from regenerating an Otto or diesel cycle engine.

Other objects, advantages, and novel features will become apparent fromthe following detailed description of the invention when considered inconjunction with the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic illustration of one embodiment of a cool pistonregenerated engine.

FIG. 2 is a schematic illustration of one embodiment of a hot pistonregenerated engine.

FIG. 3 is a schematic illustration of one embodiment of a cool pistonregenerated engine that operates on a two stroke cycle and employsexhaust means that consist of a port that is covered and uncovered bythe piston.

FIG. 4, a-h, depicts the operating sequence of a cool piston regeneratedengine operating on a two stroke cycle and having working fluid enteringthe cylinder during the compression stroke.

FIG. 5, a-h, depicts the operating sequence of a hot piston regeneratedengine operating on a two stroke cycle and having fresh working fluidentering the cylinder during the compression stroke.

FIG. 6, a-i, depicts the operating sequence of a cool piston regeneratedengine operating on a four stroke cycle and having an early closingintake valve.

FIG. 7, a-i, depicts the operating sequence of a cool piston regeneratedengine operating on a four stroke cycle and having a late closing intakevalve.

FIG. 8, a-i, depicts the operating sequence of a hot piston regeneratedengine operating on a four stroke cycle and having an early closingintake valve.

FIG. 9, a-i, depicts the operating sequence of a hot piston regeneratedengine operating on a four stroke cycle and having a late closing intakevalve.

FIG. 10, a and b, presents possible placements for the fuel injector forboth a hot piston regenerated engine and a cool piston regeneratedengine when cold side fuel injection is employed.

FIG. 11, a and b, presents possible placements for the fuel injector forboth a hot piston regenerated engine and a cool piston regeneratedengine when intake manifold fuel injection is employed.

FIG. 12, a and b, presents two possible ways to utilize the regeneratordrive rod as a means for intake and exhaust of working fluid.

FIG. 13, a-i, depicts the operating sequence of a cool pistonregenerated engine operating on a four stroke cycle.

FIG. 14, a-i, depicts the operating sequence of a hot piston regeneratedengine operating on a four stroke cycle.

FIG. 15, a-h, depicts the operating sequence of a cool pistonregenerated engine operating on a two stroke cycle.

FIG. 16, a-h, depicts the operating sequence of a hot piston engineoperating on a two stroke cycle.

FIG. 17, a and b, presents two possible ways by which regeneratormaterials having different flow passage sizes may be employed in asingle regenerator.

FIG. 18, a-e, presents a sequence of events by which a pneumatic liftermay be used to control the positioning and motion of a regenerator.

FIG. 19 presents a pneumatic lifter in a hot piston engine.

FIG. 20 shows a regenerated engine which employs a throttle as a meansto reduce the amount of working fluid which enters the cylinder.

The same elements throughout the figures are designated by the samereference characters.

DETAILED DESCRIPTION OF THE INVENTION

This invention is a regenerated, reciprocating, internal combustionengine employing a movable regenerator as described herein. All of theseembodiments of this invention employ either a two stroke cyclecomprising a compression stroke and an expansion stroke, or a fourstroke cycle comprising intake, compression, expansion, and exhauststrokes. Each stroke is accomplished by moving the piston from itsuppermost or top dead center (TDC) position, closest to the cylinderhead, to its lowermost or bottom dead center (BDC) position, furthestfrom the cylinder head, or in the reverse direction.

Each of these embodiments of this invention also has two regeneratorstrokes, a regenerative heating stroke and a regenerative coolingstroke. During the regenerative heating stroke the regenerator is movedthrough the working fluid trapped between the piston and the cylinderhead and transfers heat to this working fluid. For a cool pistonregenerated engine, the regenerative heating stroke starts with theregenerator adjacent to the cylinder head and ends with the regeneratoradjacent to and moving with the piston. For a hot piston regeneratedengine the regenerative heating stroke starts with the regeneratoradjacent to and moving with the piston and ends with the regeneratoradjacent to the cylinder head.

During the regenerative cooling stroke the regenerator moves in theopposite direction (as compared to the heating stoke) through theworking fluid trapped between the piston and the cylinder head andabsorbs heat from this working fluid. For a cool piston regeneratedengine, the regenerative cooling stroke begins with the regeneratoradjacent to and moving with the piston and ends with the regeneratoradjacent to the cylinder head. For a hot piston regenerated engine theregenerative cooling stroke begins with the regenerator adjacent to thecylinder head and ends with the regenerator adjacent to the piston.

Between the times of these motions the regenerator is either adjacentto, and moving with, the piston or, it is adjacent to the cylinder head."Adjacent to" means that the regenerator is in contact with the pistonor cylinder head or as close as possible to these components given themechanical and structural constraints associated with the comingtogether of rapidly moving objects. "Close to" is synonymous with"adjacent to". While it is advantageous to minimize any internal volumesthat are not swept by the regenerator, it must be recognized that smallclearance regions or volumes will probably be necessary to preventdamaging impacts between components and for clearances between movingcomponents. Examples of such clearance regions or volumes include smallgaps between the regenerator and the cylinder head or the piston whenthe regenerator is adjacent to these components, and the clearance gapbetween the periphery of the regenerator and the cylinder wall.

The region where combustion occurs is the hot volume or hot space andthe volume on the other side of the regenerator is referred to as thecold volume or cold space. The sizes of both of these volumes changeduring the operating cycle as the piston and regenerator move. At sometimes during the cycle each of these volumes becomes very small or zero.The side of the regenerator that is adjacent to the hot volume will bethe hottest part of the regenerator and is referred to as the hot sideof the regenerator. The opposite side is the cold side.

The working fluid that is expected to be employed in this invention isair. However, this working fluid could be any mixture of gases, liquids,and solids that can undergo an exothermic chemical reaction with thefuel. The working fluid that is introduced into the cylinder through theintake manifold is sometimes referred to as fresh working fluid. Thisfresh working fluid can contain some residual reaction products that aretrapped in the cylinder after the exhaust means close or that are addedto it in the intake manifold (i.e. exhaust gas recirculation). After thecombustion (or other exothermic reaction which provides the power forthe engine) the working fluid is referred to as spent working fluid orexhaust fluid. The fuel may be any solid, liquid, gas, or combinationsof these that can undergo an exothermic reaction with the fresh workingfluid.

FIG. 1 presents an embodiment of a cool piston, regenerated engine thatcan be operated in either a two or four stroke manner. The cylinder (1)is closed at one end by a cylinder head (2) and contains a piston (3)which is connected to a power output shaft (4) by an appropriatemechanism (5) for converting the linear motion of the piston to therotating motion of the shaft. This mechanism (5) can comprise the pistonrod and eccentric as shown in FIG. 1.

Means for the inflow and outflow of working fluid are provided by theintake valve (6) and the exhaust valve (7), which are shown asconventional poppet valves here. When open, these valves connect theintake manifold (13) and the exhaust manifold (14) to the cylindervolume located between the piston and the regenerator (8). Only theportion of these manifolds that are adjacent to the cylinder are shownin the Figures. The valves can be flush with the cylinder wall whenclosed, as is shown in FIG. 1, or they can be located some shortdistance from the cylinder and be connected to the cylinder via ports orpassages. Flush mounted valves are preferred. The intake and exhaustmeans can also be simple openings (often called ports) that are locatedin the cylinder wall and are opened and closed by being covered anduncovered by the piston, as is commonly done in small two strokeengines. However these intake and exhaust means are configured andplaced, they must communicate with the cold volume (12). "Communicatewith" as used herein means that the intake and exhaust means mustconnect with the cold volume so as to allow flow into or out of the coldvolume either directly or through one or more flow passages. For a coolpiston engine such as this, the cold volume is always located betweenthe regenerator and the piston. Thus these intake and exhaust means mustprovide flow passages through the cylinder wall, the piston, theregenerator, or combinations of these.

Inside the cylinder lies a porous disc of material referred to as theregenerator (8). This regenerator has a diameter slightly less than thecylinder bore. It is moved by a regenerator drive rod (9) back and forthbetween the piston and the cylinder head, parallel to the axis of thecylinder. The drive rod may pass through the cylinder head as shown inFIG. 1, or it may pass through the piston. In all regenerated engines,this drive rod need not be of circular cross section, nor need it besolid (i.e. it can be a tube). Other means to move the regenerator, suchas an annular sleeve between the piston and the cylinder wall, can alsobe applied to move the regenerator. No sealing means between theregenerator periphery and the cylinder wall are shown in FIG. 1.However, the use of seals, such as labyrinth seals may be advantageouslyapplied to prevent or minimize the flow of working fluid around theperiphery of the regenerator.

Fuel is injected into the hot volume by means of a fuel injector (10),such as those that are commonly employed in direct injection dieselengines. For a cool piston engine, the hot volume always lies betweenthe cylinder head and the regenerator. By injecting directly into thisregion at a time when the working fluid in this region is very hot, thefuel will be spontaneously ignited.

FIG. 2 presents a hot piston regenerated engine. This engine can operateon either a two or a four stroke cycle. This engine is very similar tothat of FIG. 1, having a cylinder (1) closed by a cylinder head (2), apiston (3) connected to a crankshaft (4) by a suitable mechanism (5),intake and exhaust valves (6 & 7) controlling flow into and out of thecylinder via intake and exhaust manifolds (13 & 14), a regenerator (8),a mechanism for moving that regenerator (9), and a fuel injector (10).

The major difference between the hot piston engine of FIG. 2 and thecool piston engine of FIG. 1 is that the combustion occurs between thepiston and the regenerator. That is, the hot volume (11) now lies belowthe regenerator and the cold volume (12) lies above it. This requiresthat the fuel injector be so positioned that the fuel can be injectedinto the hot volume. This also requires that the working fluid enter andexit the cylinder through intake and exhaust means that communicatedirectly with the cold volume in the upper part of the cylinder. Thusthese intake and exhaust means must provide a flow passage through thecylinder head, the upper part of the cylinder wall, the regeneratordrive rod (9), or combinations of these.

The regenerated engines presented in FIGS. 1 and 2 are similar inappearance to those presented in Millman's patent and the earlierpatents of Ferrenberg. However, there are substantial differencesbetween these earlier inventions and that disclosed herein. Thesedifferences are described in the following discussion.

All regenerated, reciprocating engines have a regenerative heatingstroke. This heating stroke is intended to transfer the heat stored inthe regenerator to the working fluid. All of the earlier inventions ofFerrenberg perform this regenerative heating stroke "as the pistonapproaches the top of its stroke" or "at or near the end of thecompression stroke". Furthermore, in these earlier inventions the fuelinjection always occurs after the completion of this regenerativeheating stroke. Millman states that "the regenerator remains at the topof the cylinder during fuel injection and during the power and exhauststrokes". Thus these earlier inventions have a regenerative heatingstroke that is completed prior to fuel injection and prior to the startof the piston's expansion stroke. While simple thermodynamic analysesassuming a very thin regenerator would seem to indicate that this is themost desirable timing, more recent considerations by this inventor haveshown that this sequence of events is faulty.

As the earlier patents indicate, the heating stroke should begin nearthe end of the piston's compression stroke. However, the engine'sperformance is substantially improved if the regenerative heating strokeis not completed until well into the piston's expansion stroke.Furthermore, instead of injecting the fuel after the regenerativeheating stroke, the invention disclosed herein injects the fuel duringthe regenerative heating stroke. Furthermore, the invention disclosedherein does not complete the regenerative heating stroke until well intothe piston's expansion stroke, when the pressure in the cylinder beginsto drop. This timing of the regenerative heating stroke is substantiallydifferent than that of the earlier regenerated engine inventions. Thesedifferences are not just minor overlapping of processes or slightdeviations in their timing. The invention disclosed herein has theprocesses occurring in a different order than that of the earlierinventions.

One important reason for this change in the timing of the regenerativeheating stroke involves the movement of the gases within the cylinderduring combustion. If the regenerator is adjacent to the piston or thecylinder head during fuel injection and combustion, as the earlierinventions indicate, then the rising pressure in the cylinder, due tocombustion, will force hot gases into the regenerator. As these gasesenter the regenerator they will lose heat to the regenerator, therebyreducing cylinder pressure at a time when power is being extracted. Inaddition to improved performance, the temperature of the hot side of theregenerator is reduced (an important regenerator durability issue) ifthe regenerator is moved in such a way as to prevent hot reactingcomponents of the fuel and working fluid (e.g. combusting gases) fromentering the regenerator. If the regenerative heating stroke timingproposed in the earlier inventions were applied, the regenerator wouldbe destroyed. No reasonable regenerator material could withstandexposure to those high temperatures. The new regenerative heating strokedescribed herein provides an environment in which the regenerator cansurvive and it provides for substantially improved engine performance.

In order to prevent hot combustion gases from entering the regenerator,the motion and speed of the regenerative heating stroke must be soarranged as to maintain a flow of air from the regenerator and into thehot volume. This acts as a form of transpiration cooling for the hotsurface and also prevents the very hot working fluid in the hot volumefrom entering the regenerator. If flow from the hot side of theregenerator (the side facing the region where combustion is occurring)is to be maintained throughout the regenerative heating stroke, then itis necessary that the regenerator move at such a speed as to prevent thepressure in the hot volume from exceeding that in the regenerator. Thisrequires a careful and coordinated timing of the heat release rate (thefuel injection rate) and the motion of the regenerator. Once thepressure in the cylinder begins to drop during the expansion, the flowwill always be out of the regenerator. This is because the working fluidwithin the regenerator will be expanding into the lower pressure hotvolume, thereby maintaining a steady flow of working fluid out of thehot end of the regenerator.

During the compression stroke, working fluid is being compressed anddriven into the regenerator. Initially this working fluid is cool andabsorbs heat from the regenerator. However, near the end of thecompression stroke, the air entering the regenerator is nearly as hot asthe cold side of the regenerator. The compression of the air within theregenerator causes its temperature to exceed that of the regenerator.The effect of all this is that the net heat transfer from theregenerator becomes negative--that is, the regenerator is absorbing heatfrom the compressed working fluid. This is, of course, very undesirableand can be prevented by beginning the regenerative heating stroke atabout the time this occurs. When the regenerator starts to move, theflow of large amounts of the slightly cooler working fluid into theregenerator results in much more heating of the working fluid, therebyproducing a strongly positive heat transfer. Thus the regenerativeheating stroke must begin during the final portion of the compressionstroke.

In summary, the optimum motion and timing of the regenerative heatingstroke should be as follows:

(1) Start the heating stroke at about the time that the heat transferfrom the regenerator becomes negative (during the last quarter of thepiston's compression stroke).

(2) Maintain the motion of the regenerator at such speeds that the flowof working fluid is always into the hot volume.

(3) Complete the regenerative heating stroke as soon as possible afterthe pressure in the cylinder begins to drop during the expansion stroke(usually within a few tens of degrees after TDC, but this is highlydependent upon the fuel injection rate and other factors).

These differences in the regenerative heating stroke between theregenerative engine disclosed herein and those of the earlier inventionsof Ferrenberg and Millman have a large effect on the performance of theengine and the durability of the regenerator. Without these improvementsthe regenerated engine would not be feasible.

Another important and novel feature of the regenerated engine inventiondisclosed here, that is substantially different from the earlierinventions of Ferrenberg and Millman, is its regenerative coolingstroke. At some point during the piston's expansion stroke, theregenerator sweeps through the working fluid in the cylinder andextracts energy from it. This is the regenerative cooling stroke.Computations performed by this inventor clearly show that the optimumtime to begin this regenerative cooling stroke is at about the time thepiston's expansion stroke is half completed.

Millman's regenerated engine does not have a regenerative coolingstroke. The regenerator is simply held in a stationary position close tothe valves in the cylinder head while the exhaust valve opens and therapid depressurization (the "blowdown") occurs. The hot gases blowdownthrough the regenerator.

The earlier regenerated engine inventions of Ferrenberg do not start theregenerative cooling stroke until "the piston is near bottom deadcenter". By starting the regenerative cooling stroke near the middle ofthe piston's expansion stroke, the regenerated engine inventiondisclosed here is substantially different from and superior to theearlier inventions. The reason for this is discussed in the following:

As the regenerator sweeps through the working fluid during its coolingstroke, it cools the working fluid which reduces the pressure. As thepressure drops, the work output of engine is reduced. Thus it would seemto be desirable to delay this cooling stroke until the expansion isnearly complete and as much work as possible has been extracted from theworking fluid. This is the basis for delaying the start of theregenerative cooling stroke until near the end of the expansion strokein the earlier inventions of Ferrenberg. However, more recent anddetailed computations have been performed that include the work requiredto move the regenerator. This work increases quite rapidly as theregenerator's cooling stroke length and speed are increased. Thus itbecomes necessary to "trade off" the additional thermodynamic workprovided by a full expansion prior to regenerative cooling, vs. theextra work required to move the regenerator. The computations indicatethat a regenerative cooling stroke that begins near the middle of thepiston's expansion stroke provides optimum performance.

These same computations indicate that engine performance is improved ifthis regenerative cooling stroke is completed, or nearly completed,before the exhaust means opens. This is important because if theblowdown occurs prior to the regenerator completing its sweep throughthe cylinder, the working fluid remaining within the hot volume expandsand is cooled. This expanded working fluid can become cooler than thehot side of the regenerator and thus actually remove heat from thehotter portions of the regenerator as it passes through the regenerator.This is very undesirable as it substantially reduces engine power andefficiency. Because Millman's engine has no regenerative cooling stroke,and because the earlier inventions of Ferrenberg all open the exhaustmeans long before the completion of the regenerative cooling stroke,substantial blowdown through the regenerator occurs. The new inventiondisclosed herein prevents this by completing the regenerative coolingstroke prior to the opening of the exhaust means.

In summary, the detailed computations have shown that the regenerativecooling stroke should:

(1) begin during the middle half (between 45 and 135 degrees after topdead center) of the start of the expansion stroke, and

(2) end prior to the opening of the exhaust means.

There is, of course, some flexibility in these guidelines. Second ordereffects not yet analyzed and other engine design and operationalconsiderations could affect them. For example, by moving the regeneratormore slowly during the cooling stroke, the power required to move theregenerator is reduced. Therefore, it might be advantageous to delay thecompletion of the regenerative cooling stroke until very shortly afterthe exhaust means are open. Whether or not this is advantageous ishighly dependent upon the engine geometry, valve timing, and otherfactors. But in any case, the regenerative cooling stroke should be verynearly complete prior to the opening of the exhaust valve.

The previous regenerated engine inventions of Ferrenberg (U.S. Pat. Nos.4,790,284 and 4,928,658) that operated with valves, never had the intakeand exhaust valves open at the same time. The intake valve wasspecifically closed prior to the opening of the exhaust valve. Theinvention of Millman (U.S. Pat. No. 4,280,468) differs from theinvention disclosed herein in many ways, most especially and veryimportantly in the lack of a regenerative cooling stroke. Millman makesno mention of valve opening and closing times, but his Figures implythat the exhaust closes before the intake opens. This is a seriousdeficiency in these earlier inventions. Regenerated engines have aspecial and critical need for valve overlap.

At moderate to high engine speeds the inertia of valve mechanicalcomponents, the inertia of the working fluid in the cylinder, and theshorter time available for the intake and exhaust processes, make itadvantageous to maintain the exhaust valve in an open position for ashort while after the intake valve opens. This will occur near the endof the exhaust process and the beginning of the intake process.

Keeping the exhaust valve open for a short while after the intake valveopens also improves the removal of spent working fluid. This isespecially important in a regenerated engine as some exhaust fluid willremain trapped in the regenerator anyhow. Also, the presence of theregenerator can retard the gas exchange processes. Excessive retainmentof exhaust fluid can degrade engine performance. By minimizing thetrapped exhaust fluid, via overlapping valve openings, this performancedegradation can be minimized.

For most operating conditions and fuel types, the temperature of theworking fluid in the hot volume and the temperatures of the internalsurfaces adjacent to that volume, at the time of fuel introduction, willbe sufficient to rapidly ignite the fuel. Thus, an ignition source willnot normally be required for a regenerated engine. It is anticipatedthat an ignition source will not even be required for starting, asappropriate motion of the regenerator and the compression of the air, orother means, will be sufficient to heat the regenerator and cylinder toignition temperatures. Thus the regenerated engine invention disclosedherein has no specific ignition means (e.g. a spark plug or a glowplug)

In the earlier regenerated engine inventions of Ferrenberg, "all of theengine embodiments presented herein utilize a spark plug for ignition ofthe fuel". While recognizing that this ignitor may only be required forstarting, such an ignition source is included in every embodiment andclaim.

The earlier patent of Ferrenberg shows the preferred embodiment of thecool piston engine as having a piston that has its rings located farfrom the face of the piston in order to accommodate "a large annularclearance between itself and the cylinder", or "slots or other types offlow passages". The invention disclosed herein has a more conventionalpiston with a flat face and rings close to the face of the piston. Thisis done in recognition of the fact that the intake and exhaust means orthe passages between these means and the cylinder can be located higheron the cylinder wall. Thus, flow around or through the piston is notrequired.

Computations performed by this inventor show that the efficiency of aregenerated engine improves as more energy is regeneratively transferredbetween the expanded combustion products and the compressed workingfluid. The greater the temperature difference across the regenerator,the greater is this heat transfer and hence, engine efficiency.

Now, the regenerator's hot end temperature is primarily determined bythe temperature of the combustion products that pass through it duringthe regenerator's cooling stroke. The temperature of the cold side ofthe regenerator is primarily determined by the temperature of thecompressed working fluid that passes through it during the regenerator'sheating stroke.

One way to increase this temperature difference is to cool the workingfluid during the compression stroke. The ideal situation would be anisothermal compression. This will result in cooler compressed workingfluid at the time the regenerator's heating stroke occurs and a greatertemperature difference across the regenerator. This will increase theamount of regenerative heating and improve engine fuel efficiency.Isothermal compression also reduces the engine's compression work.

Given that the benefits of near isothermal compression in a regeneratedengine are very great, it is now necessary to conceive of some means bywhich this near isothermal compression can be accomplished. One means bywhich this can be done is by performing a portion of the compression ata separate location from the rest of the cycle--that is, outside thecylinder. This eliminates much of the heating from cylinder walls thathave been heated by combustion and allows the use of special coolingfeatures in the compressing device that would not be possible in anengine where the compression and combustion occur in the same cylinder.Examples of these cooling features are: (a) thin walled, highlyconductive materials in the compressor to remove heat, (b) cooling fins,perhaps with liquid coolant flowing through them, that are in directcontact with the working fluid as it is being compressed, (c) coolingfins on the exterior surfaces of the compression device, and (d) the useof aftercoolers in the flow passage between the compression device andthe engine cylinder.

This external compressor could be another cylinder and piston,turbomachinery (e.g. a supercharger or a turbocharger), or other devicesthat can efficiently produce high pressure air in sufficient quantity.This compressor could "feed" several cylinders of a multi-cylinderregenerated engine.

It must be made clear that this is not simply a highly turbocharged orsupercharged regenerated engine. The intent here is to replace some ofthe compression that occurs in the cylinder with compression in anexternal, cooled, compressor. The timing of the intake means is thenadjusted so as to reduce the compression of the working fluid thatoccurs within the cylinder of the engine. For example, by delaying theintroduction of much of the working fluid until the piston's compressionstroke is partially complete, the effective compression is reduced.

The most important feature of this movable regenerator, regeneratedengine employing external compression is that the effective compressionratio in the cylinder is less than the effective expansion ratio in thecylinder. The effective compression ratio is the volume occupied by theworking fluid at the start of the compression divided by the volumeoccupied by the working fluid at the completion of the compression. Thestart of the compression is essentially the time when the intake valveor port closes and the pressure in the cylinder begins to rise. The endof compression is the time when the piston's compression stroke iscompleted. The expansion ratio is the volume of the working fluid at theend of the expansion stroke divided by the volume at the start of theexpansion stroke. The expansion stroke is completed when the exhaustmeans open or the piston attains its bottom dead center position.

A regenerated engine employing this concept of external compression andlesser effective compression than expansion ratios operates in the samemanner as other regenerated engines. The only major difference is thetiming of the intake means and the generally much higher pressure in theintake manifolds. This concept can be applied in both two or four strokeoperation, and it can be applied to both hot piston and cool pistonregenerated engines.

FIG. 3 presents a special type of cool piston regenerated engineemploying external compression and an effective compression ratio thatis less than the effective expansion ratio. This engine operates on atwo stroke cycle. This engine has all the same components as the coolpiston engine depicted in FIG. 1, except that the exhaust valve isreplaced by a port (7) that is uncovered (opened) by the piston as itapproaches its lowest position (bottom dead center), and subsequentlycovered (closed) by the piston shortly after it starts upward on itscompression stroke. These exhaust means could also be one or morevalves.

The engine of FIG. 3 is intended to operate with high pressures in theintake manifold. These pressures are to be provided by the use ofcompressors (not shown in FIG. 3), either singly or staged, that arepowered by: (a) turbines that extract energy from the engine's exhaustgases (turbochargers) or (b) direct power take-off from the engine'scrankshaft (supercharger). The compressor may be of sliding vane,centrifugal, or rotary types, including roots blowers and comprexsuperchargers, as well as conventional piston in cylinder compressors.

FIG. 4, a-h, presents the sequence of steps or processes occurring in atwo-stroke cycle, cool piston, regenerated engine employing this conceptof external compression and an effective compression ratio that is lessthan the effective expansion ratio. This engine is essentially the sameengine as was depicted in FIG. 3, however, only the primary componentsof this engine are shown in FIG. 4. These are the cylinder (1), thecylinder head (2), the piston (3), the intake valve (6) the exhaustvalve (7) the regenerator (8), the regenerator drive rod (9), and thefuel injector (10).

Referring to FIG. 4, at the start of the compression stroke (a) theexhaust port is open, the intake valve is closed, the regenerator is atthe top of the cylinder, and the piston is at its BDC position. The hotside of the regenerator is adjacent to the cylinder head and the coldside faces the piston. Near the time that the piston begins to moveupward in its compression stroke (b) the intake valve opens. For a shorttime both the intake valve and the exhaust port are open and the highpressure, fresh working fluid in the intake manifold forces most of thespent working fluid remaining in the cylinder out through the exhaustport. As the piston rises, the exhaust port is covered (c). As thepiston continues to rise, the intake remains open for some time, therebyallowing additional pressurized working fluid to enter the cylinder.When the pressure in the cylinder rises to about the level in the intakemanifold the intake valve closes (prior to d). Ideally, the pressure inthe cylinder and the pressure in the intake manifold should be equalwhen the intake valve closes.

As the piston approaches its TDC position, the regenerator begins tomove from the top of the cylinder down toward the piston (d). As it doesthis, the compressed working fluid is forced through the regenerator,into its cold side and out of its hot side, and absorbs heat from it.Fuel is injected into the newly formed hot volume in the cylinderbetween the moving regenerator and the cylinder head (e). This fuel isignited by the high temperatures in the hot volume and reacts with theworking fluid. The regenerator continues downward and meets the pistonat some point (e.g. 10-60 degrees) after TDC (f). Ideally, theregenerator should meet the piston shortly after the pressure in thecylinder begins to drop during the expansion. The regenerator thenfollows the piston down during the expansion stroke (g), separating fromit at some point long before the piston reaches BDC, and begins totravel back toward the cylinder head (h). The exhaust port is uncoveredby the piston at about the time the regenerator approaches the top ofthe cylinder. This completes the two-stroke cycle.

FIG. 5, a-h, presents the sequence of events for a two stroke cycle, hotpiston, regenerated engine employing external compression and aneffective compression ratio that is less than the effective expansionratio. This engine is the same as that of FIG. 2 except that the exhaustvalve of FIG. 2 has been replaced by an exhaust port (7) in FIG. 5. Theengine shown in FIG. 2 could also accomplish the cycle described here.

At the start of the compression stroke (a), the piston is at its BDCposition, the exhaust port is uncovered, the regenerator is adjacent tothe piston, and the intake valve is closed. The hot side of theregenerator is closest to the piston and the cold side faces thecylinder head. As the piston and regenerator begin to move upward, theintake valve opens (b) and pressurized working fluid enters thecylinder, pushing out the spent working fluid. As the piston andregenerator rise further, the exhaust port is covered (c). Fresh workingfluid continues to enter the cylinder until the pressure isapproximately equal to that in the intake manifold. The valve thencloses (d).

As the piston and regenerator approach the top of the cylinder, theregenerator begins to move away from the piston and toward the cylinderhead (e). As the regenerator moves, the compressed working fluid isforced through the regenerator, from the cold side to the hot side. Asthe working fluid moves through the regenerator it absorbs heat from it.Fuel is then injected into the hot volume between the moving regeneratorand the piston (f). The piston completes its compression stroke andbegins its expansion stroke. During the first quarter of the pistonsexpansion stroke, the regenerator reaches the cylinder head and remainsadjacent to the cylinder head. When the piston is in the middle portionof its expansion stroke, the regenerator begins to move down toward thepiston (g). The regenerator overtakes the piston at about the time thepiston uncovers the exhaust port (h).

Both versions of this external compression, lower effective compressionthan expansion ratio, regenerated engine require that the fresh workingfluid be introduced into the cylinder during the piston's compressionstroke. In order to provide sufficient flow into the cylinder during therelatively short time available for intake flow, several and largeintake valves could be used.

For either the cool piston or the hot piston version of this externalcompression, lower effective compression than expansion ratio,regenerated engine, if the pressure provided by the external compressoris reduced, then the power of the engine will be reduced. However, thefuel efficiency of the engine will still be high. This is because (1) agreater expansion to compression ratio is thermodynamically moreefficient, and (2) the lower post compression temperatures provide forgreater regenerative heat transfer, which further improves efficiency.Thus a lower effective compression ratio than expansion ratio isespecially beneficial for a regenerated engine. Even if the externalcompressor is eliminated (i.e. a naturally aspirated engine), thebenefits of this approach are substantial.

It should also be noted that in either of the engines presented in FIG.4 or 5, if the intake valve is kept open after the intake and cylinderpressures are equal, the flow through the intake valve will be reversed.This will result in the expulsion of some of the fresh working fluid anda further reduction in effective compression ratio. This will reducepower, but will provide high efficiency. A similar effect can beobtained by closing the valve before the pressures are equal.

This same approach of utilizing an effective compression ratio that isless than the effective expansion ratio can also be employed in fourstroke cycle regenerated engines. This is depicted in FIGS. 6 through 9.

FIG. 6, a-i, depicts the sequence of steps required to perform a fourstroke cycle with an effective compression ratio less than that of theexpansion ratio, in a cool piston regenerated engine. This reduction incompression ratio is accomplished by closing the intake valve during theintake stroke, thereby reducing the amount of working fluid that wouldbe in the cylinder if the intake closing were delayed. The engine designshown in FIG. 6 for this description of the engine processes is the sameas that of FIG. 1.

At the start of exhaust stroke (a), the piston is at its BDC position,the regenerator is adjacent to the cylinder head, the intake valve isclosed, and the exhaust valve has just opened. The piston now moves toits TDC position, which lies just below the valves. This is the exhauststroke whereby spent working fluid is expelled from the cylinder. As thepiston approaches the end of this exhaust stroke, the intake valve isopened (b). The exhaust valve is closed as the piston begins to movetoward its BDC position, thereby performing an intake stroke wherebyfresh working fluid is drawn into the cylinder. At some point duringthis intake stroke (c) the intake valve is closed. By closing this valveearly, the amount of working fluid contained within the cylinder isreduced from what it would have been had the intake valve remained openlonger. This is the essential and most unique feature differentiatingthis operating cycle from that of other four stroke, regenerated engineoperating cycles.

The piston continues its movement toward the bottom of the cylinder (d).The piston then moves from its BDC position to its TDC position, therebyperforming a compression stroke whereby the working fluid is compressed.As the piston nears its TDC position, the regenerator begins to moveaway from the cylinder head and toward the piston (f). As it moves, theworking fluid passes through the regenerator, from the cold volume belowthe regenerator to the hot volume above it. As the working fluid passesthrough the regenerator, it absorbs heat from the regenerator. Fuel isinjected into the hot volume above the moving regenerator as the pistonapproaches its TDC position and begins to move downward in itssubsequent expansion stroke (g). The regenerator moves downward fasterthan the piston and meets it during the first quarter of the piston'sexpansion stroke (h). The regenerator then moves with the piston awayfrom the cylinder head. During the middle part of the piston's expansionstroke the regenerator reverses its direction and begins to move backtoward the cylinder head (i). As it moves through the exhaust fluid, thehot exhaust fluid passes through the regenerator, from the hot to thecold side, and gives up heat to the regenerator. The regenerator reachesthe cylinder head at about the time that the exhaust valve opens.

FIG. 7, a-i, depicts the sequence of steps required to perform a fourstroke cycle with an effective compression ratio less than that of theexpansion ratio, in a cool piston regenerated engine. This reduction incompression ratio is accomplished by keeping the intake valve openduring a substantial portion of the compression stroke, causing some ofthe fresh working fluid to be forced out of the cylinder and therebyreducing the amount of working fluid in the cylinder. The engine designshown in FIG. 7 for this description of the engine processes is the sameas that of FIG. 1.

Referring to FIG. 7, the exhaust stroke and the first portion of theintake stroke (a to b to c) are identical to those of FIG. 6. However,in FIG. 7, the intake valve remains open throughout the intake strokeand into the subsequent compression stroke (d to e). After some of theworking fluid has been forced back into the intake manifold (e), theintake valve closes. The remainder of the cycle (f to i) is identical tothat of FIG. 6.

FIG. 8, a-i, depicts the sequence of steps required to perform a fourstroke cycle with an effective compression ratio less than that of theexpansion ratio, in a hot piston regenerated engine. This reduction incompression ratio is accomplished by closing the intake valve during theintake stroke, thereby reducing the amount of working fluid that wouldbe in the cylinder if the intake closing were delayed. The engine designshown in FIG. 6 for this description of the engine processes is the sameas that of FIG. 2.

At the start of the exhaust stroke (a), the piston is at its BDCposition, the regenerator is adjacent to the piston, the intake valve isclosed, and the exhaust valve is open. The hot side of the regeneratoris facing the piston and the cold side is facing the cylinder head. Thepiston then moves to its TDC position, thereby forcing spent workingfluid out of the cylinder through the exhaust valve. The regeneratorremains adjacent to the piston. Near the completion of the exhauststroke (b), the intake valve opens, permitting the flow of fresh workingfluid into the cylinder. The exhaust valve closes as the piston beginsto move toward its BDC position, thereby performing an intake strokewhereby additional fresh working fluid enters the cylinder (c). Theregenerator remains adjacent to the piston. At some time during thisintake stroke the intake valve closes (d), thereby reducing the amountof working fluid that would enter the cylinder if the intake valve hadremained open longer. This is the crucial and most novel step in thisprocess.

After the intake stroke, the piston moves from its BDC position (e) toits TDC position, thereby performing a compression stroke. Theregenerator remains adjacent to the piston until near the end of thiscompression stroke. At that point it begins to move away from the pistonand toward the cylinder head (f). Fuel is introduced into the regionbetween the moving regenerator and piston as the piston completes itscompression stroke and begins it subsequent expansion stroke (g). Theregenerator reaches the cylinder head during the first quarter of thepiston's expansion stroke (h) and remains adjacent to the head until thepiston is near the middle of its expansion stroke. The regenerator thenmoves toward the piston (i), reaching and remaining adjacent to thepiston as the piston approaches its BDC position. This completes thecycle.

FIG. 9, a-i, depicts the sequence of steps required to perform a fourstroke cycle with an effective compression ratio less than that of theexpansion ratio, in a hot piston regenerated engine. This reduction incompression ratio is accomplished by keeping the intake valve openduring a substantial portion of the compression stroke, causing some ofthe fresh working fluid to be forced out of the cylinder and therebyreducing the amount of working fluid in the cylinder. The engine designshown in FIG. 9 for this description of the engine processes is the sameas that of FIG. 2.

Referring to FIG. 9, the exhaust stroke and the first part of the intakestroke (a to b to c) are identical to that of FIG. 8. Now, however, theintake valve remains open throughout the intake stroke and into thesubsequent compression stroke (c to d). After some of the working fluidhas been forced back into the intake manifold (d), the intake valvecloses (e). The remainder of the cycle (f to i) is identical to that ofFIG. 8.

All previous regenerated engine inventions are direct injection types,that is, the fuel is directly injected into the combustion region (thehot volume) of the cylinder. (Millman mentions a "carburetted" engine inconnection with his hot piston regenerated engine. However, his enginelacks a regenerative cooling stroke, which makes it substantiallydifferent from, and inferior to, the regenerated engine inventiondisclosed herein.) It is also possible to introduced the fuel at otherlocations. Such approaches would include injection of fuel into thecylinder on the cold side of the regenerator, injection of the fuel intothe working fluid in the intake manifold prior to its passage into thecylinder, and the use of conventional carburetors or other devices toatomize and vaporize the fuel and mix it with the working fluid prior toentering the intake manifold.

It is important to recognize that the location of injection need not bethe same as the location where combustion occurs. When direct injectioninto the combustion region is not employed, the mixture of reactants(i.e. the fuel and the air) must, for the most part, pass through theregenerator prior to the major release of heat from it. Since there isno flow through the regenerator until the start of the regenerativeheating stroke, and since the combustion should begin at about (orslightly after) the start of this heating stroke, it may be possible toprovide a means for igniting the mixture that is based upon theinitiation of this flow through the regenerator.

The hot side of the regenerator itself can serve as the ignition sourcefor the mixture of reactants. The problem with this approach is that themixture is in contact with the hot parts of the regenerator long beforeignition is desired. Therefore, some feature must be provided thatprevents ignition until the desired time. There are severalpossibilities. First, since the hot volume does not exist until thestart of the regenerative heating stroke, the reactants exposed to thehot side of the regenerator will be trapped within the regenerator'sporous structure. If these pores are sufficiently small, they will actlike a flame arrestor and prevent (or delay) the ignition of themixture. Then when the regenerator begins to move (the start of theheating stroke), the very hot mixture will be transported out of theregenerator where it will spontaneously react.

Another factor which will tend to delay ignition until the proper timeis the compressive heating and the increase in pressure of the mixtureof reactants that is occurring during the compression stroke. As thepressures and overall reactants' temperatures rise near the end of thecompression stroke and the start of the regenerative heating stroke, themixture will react more rapidly, thereby providing for timely ignition.In combination with the release of the mixture from the reactionquenching effects of the regenerator, this would provide a simple meansby which ignition could be obtained.

Finally, an ignition source, such as a glowplug or spark plug, locatedon the hot side of the regenerator (i.e. in the hot volume) may be usedto ignite the mixture of reactants flowing through the regenerator.

FIG. 10 presents the two regenerated engines of FIGS. 1 and 2 with thefuel injector (10) moved so as to inject fuel into the cold volume (12).(For the hot piston engine the cold volume lies above the regeneratorand for the cool piston engine the cold volume lies below theregenerator.) This provides for the direct injection of fuel into theworking fluid in the cold volume. This injection can occur at any timeafter the exhaust valve closes, that is, during the intake stroke or thecompression stroke. This approach can also be applied to two strokeregenerative engines, engines employing one or more ports instead ofvalves, engines that have effective compression ratios that are lessthan their effective expansion ratios, engines with boosted intakemanifold pressures, and all other types of regenerated engines.

FIG. 11 presents the two regenerated engines of FIGS. 1 and 2 with thefuel injector (10) moved so as to inject fuel into the intake manifold(13). In this way the fuel is vaporized and atomized and transportedinto the cylinder with the working fluid as it enters the cold volume(12) through the intake valve (6). The fuel could also be introduced atother locations in the intake manifold. It could also be introduced intothe working fluid by conventional carburetors. This approach can also beapplied to two stroke regenerative engines, engines employing one ormore ports instead of valves, engines that have effective compressionratios that are less than their effective expansion ratios, engines withboosted intake manifold pressures, and all other types of regeneratedengines.

One major concern with most regenerated engine designs is the placementand size of the intake and exhaust means. In all regenerated engines,the working fluid must flow into and out of the cold volume. For a coolpiston regenerated engine this means that the flow passages must be inthe piston, the cylinder wall below the cylinder head, the regenerator,or combinations of these. None of these are common in conventionalengines, although engines having ports in the wall of the cylinder thatare covered and uncovered by the piston are common for many two strokeengines. Placing valves in the cylinder wall, especially flush mountedvalves as have been shown in many of the previous Figures, would be adifficult and challenging task.

For hot piston regenerated engines, the valves can be placed in thecylinder head, a more conventional placement. However, if theregenerator drive rod also penetrates the head, the space available forthese valves will be reduced. Since larger valves are always desirablefor improved volumetric efficiency, this could present a problem.

In order to improve this valve sizing and placement situation for bothhot and cold piston engines, the regenerator drive rod can be used as ameans to flow working fluid into, out of, or into and out of, thecylinder. This can be accomplished by using a tube as the regeneratordrive rod and suitably connecting it to the intake or exhaust manifolds,or both. It is expected that the flow through the tube will only providea portion of the intake or exhaust flow, and probably not both. However,it is possible that all of the intake flow or exhaust flow or both couldbe provided by a drive rod with a sufficiently large inside diameter orby multiple drive rods. A single rod that provides both intake andexhaust flow is shown in FIG. 12.

FIG. 12 presents two different versions of a regenerator drive rod thatalso functions as a means to intake and exhaust working fluid. Each ofthese Figures shows the two ends of the drive rod. The two versionsshown are applicable to the two possible situations: (12a) theregenerator drive rod attaches to the regenerator from the hot side ofthe regenerator (i.e. the rod passes through the hot volume), and (12b)the regenerator drive rod attaches to the regenerator from the cold sideof the regenerator (i.e. the rod passes through the cold volume). Forexample, configuration (12a) could be applied to a cool pistonregenerated engine with the drive rod entering the cylinder through thecylinder head.

Referring to FIG. 12a, the regenerator (8) is attached to the drive rod(9) by means of a structure (20) which is shown here as a flangeattached to the lower end of the drive rod and embedded in the cold sideof the regenerator. The rod (actually a tube) passes through theregenerator and provides an opening (29) from its interior to the coldvolume on the cold side of the regenerator. The interior of the tubecontains a flow control device hereafter referred to as a check valve(21). This check valve only permits flow through the rod (in eitherdirection) when the pressure in the cylinder is equal to, or onlyslightly greater than, the pressure in the upper part of the drive rod.That is, the valve is open during the intake and exhaust strokes whenthe pressure in the cylinder is relatively low.

Near the other end of the drive rod, the rod has openings (26 and 27)that are connected by valves (22 and 23) to the intake manifold (24),and the exhaust manifold (25). At the appropriate times in the engine'soperating cycle either the intake valve (22) or the exhaust valve (23)will be open. If the pressure in the cylinder is low enough, and ifeither of the valves is open, then flow through the rod will occur.

In FIG. 12b, the regenerator (8) attaches to the rod (9) via a structure(20) that is shown here as a flange attached to the lower end of thedrive rod and imbedded in the cold side of the regenerator. Since theflow through the rod must enter and exit the cold volume, holes (28) areprovided in the tube at some location above the regenerator attachpoint. The end of the tube is closed so that no flow passes into orthrough the regenerator. The check valve (21) and the upper end of thedrive rod are identical to that of FIG. 12a.

The use of the regenerator drive rod as a means for intake flow isespecially useful when applied to the cool piston, two stroke,regenerated engine of FIG. 3. In this case the flow through the driverod can replace all, or a part of, the flow through the intake valve. Ifthe drive rod provides the only intake flow path, then the intake valveshown in FIG. 3 will be eliminated. Since the regenerator is at the topof the cylinder throughout the intake and exhaust processes, thescavenging provided by having flow entering at the center and top of thecylinder and exiting at the bottom periphery is excellent. Vanes andother flow dispersion or swirl devices can be added within the drive rodif desired to further promote scavenging.

In a regenerated engine it is important that the regenerator be able tosweep through all of the internal cylinder volume. If regions existwithin the cylinder that the regenerator cannot pass through, then theseregions can "shelter" a part of the working fluid from the regenerativeheating and cooling processes. Compressed working fluid that is trappedin these regions cannot be regeneratively heated, and hot exhaust fluidstrapped in these regions cannot have their thermal energy extracted bythe regenerator. This reduces the efficiency of the engine.

Now, previous cold piston regenerated engines operating with valves(Ferrenberg, U.S. Pat. Nos. 4,790,284 and 4,928,658) placed these valvesin passages that were connected to the cylinder. These passages sheltera portion of the working fluid, as previously discussed, therebysubstantially reducing engine performance. Accordingly, it is highlydesirable to minimize the size of these passages. One way to do this isto mount the valves so that they are flush with the cylinder wall whenclosed. Flush mounting implies that the valves will perfectly conform tothe shape of the internal wall of the cylinder, thereby providing flowpassages of zero volume between the valves and the cylinder. This is whyall of the valves shown in all of the Figures are flush mounted.

It must be recognized that perfect flush mounting is a goal and thatsome deviation from this can be accepted with minimal performancelosses. For example, in order to use flat bottomed, round, poppet valvesa flat region could be made in the interior wall of the cylinder thatwould accommodate and seat the valve. This would provide only a verysmall region that could not be swept by the regenerator. Valves that areflush mounted in the cylinder wall, or are nearly flush mounted as justdescribed, are referred to as "flush mounted" or "substantially flushmounted" valves. For purposes of this patent application, these twodescriptions have the same meaning.

Ports or openings in the cylinder wall or an annular sleeve alsoeffectively act as flush mounted valves in that they provide no volumethat can shelter working fluid from the regenerator.

Valves in the cylinder wall may be so located that the piston face orthe piston rings may or may not pass over them. Valve timing will, ofcourse, be critical, especially if they are so located that the pistoncan impact them when open. It may also be possible to employ valves thatopen outward from the cylinder. Finally, the valves of any of theengines discussed herein can be operated by a variety of mechanisms,including conventional or hydraulic lifters and rocker arms, valvemechanisms that provide variable timing (as a function of engine speedor load), and electromechanical (solenoid operated) mechanisms.

Valve opening overlap, realistic and feasible regenerator heating stroketiming and motion, the use of a regenerative cooling stroke, andrealistic and feasible regenerator cooling stroke timing and motion areall included in the regenerated engine operating sequences shown inFIGS. 13-16. The operating sequences presented in these Figures differfrom those of FIGS. 4-9 in that these engines are not intended to haveeffective compression ratios that are substantially different from theeffective expansion ratios.

FIG. 13, a-i, presents the sequence of operations of a cool piston,regenerated engine operating on a four stroke cycle. The engine shown isthe same as that of FIG. 1, but only the major components are shown.These are: the cylinder (1), the cylinder head (2), the piston (3), theintake valve (6), the exhaust valve (7), the regenerator (8), theregenerator drive rod (9), and the fuel injector (10).

The sequence starts with the piston near its BDC position, theregenerator adjacent to the cylinder head, the intake valve closed, andthe exhaust valve having just opened (a). The piston then moves to itsTDC position thereby performing an exhaust stroke whereby spent exhaustfluid is forced out the exhaust valve. Near the end of this exhauststroke the intake valve opens (b). The piston then begins to move awayfrom its TDC position in its intake stroke. The exhaust valve closes (c)and the piston then moves to its BDC position, thereby completing theintake stroke and introducing fresh working fluid into the cylinder.During the early part of the piston's subsequent compression stroke, theintake valve remains open (d). It only remains open for a long enoughtime to assure that as much working fluid as possible has entered thecylinder. It is not intended that it stay open long enough for workingfluid to be forced back out the intake valve (as was the case for theengine operation presented in FIG. 7).

The intake valve then closes and the piston proceeds to perform theremainder of its compression stroke (e). Just before the completion ofthis compression stroke the regenerator begins to move away from thecylinder head and toward the piston in its regenerative heating stroke(f). As the piston completes its compression stroke and begins itsexpansion stroke, fuel is injected into the space between the movingregenerator and the cylinder head (g). As the fuel reacts with theworking fluid and the piston continues its expansion stroke, theregenerator continues to move toward the piston. The motion and timingof this portion of the regenerative heating stroke are such that theflow through the regenerator is always toward the hot volume, where thefuel is reacting. During the first quarter of the piston's expansionstroke, the regenerator overtakes the piston and continues to move withit (h). When the piston's expansion stroke is about half complete, theregenerator reverses its direction and begins to move back toward thecylinder head in its regenerative cooling stroke (i). The regeneratorcompletes this cooling stroke as the piston approaches its BDC positionand the exhaust valve opens. This completes the operating cycle.

FIG. 14, a-i, presents the sequence of operations of a hot piston,regenerated engine operating on a four stroke cycle. The engine shown isthe same as that of FIG. 2, but only the major components are shown.These are: the cylinder (1), the cylinder head (2), the piston (3), theintake valve (6), the exhaust valve (7), the regenerator (8), theregenerator drive rod (9), and the fuel injector (10).

The operating cycle begins with the piston at its BDC position, theregenerator adjacent to the piston, the intake valve closed and theexhaust valve having just been opened (a). The piston then moves to itsTDC position, thereby performing an exhaust stroke whereby the spentworking fluid is expelled from the cylinder. The regenerator remainsadjacent to the piston throughout this exhaust stroke. Near thecompletion of this exhaust stroke the intake valve opens (b). The pistonthen moves from its TDC position to its BDC position, thereby performingan intake stroke and introducing fresh working fluid into the cylinderthrough the intake valve. Near the start of this intake stroke theexhaust valve is closed (c). The regenerator remains adjacent to thepiston throughout this intake stroke. During the early part of thepiston's subsequent compression stroke, the intake valve remains open(d). It only remains open for a long enough time to assure that as muchworking fluid as possible has entered the cylinder. It is not intendedthat it stay open long enough for working fluid to be forced back outthe intake valve (as was the case for the engine operation presented inFIG. 9).

The intake valve then closes and the piston proceeds to perform theremainder of its compression stroke (e). The regenerator remainsadjacent to the piston. Just before the completion of this compressionstroke the regenerator begins to move away from the piston and towardthe cylinder head in its regenerative heating stroke (f). As the pistoncompletes its compression stroke and begins its expansion stroke, fuelis injected into the space between the moving regenerator and the piston(g). As the fuel reacts with the working fluid and the piston continuesits expansion stroke, the regenerator continues to move toward thecylinder head. The motion and timing of this portion of the regenerativeheating stroke are such that the flow through the regenerator is alwaystoward the hot volume, where the fuel is reacting. During the firstquarter of the piston's expansion stroke, the regenerator reaches thecylinder head and remains adjacent to it (h). When the piston'sexpansion stroke is about half complete, the regenerator begins to moveback toward the piston in its regenerative cooling stroke (i). Theregenerator completes this cooling stroke, reaching and remainingadjacent to the piston, as the piston approaches its BDC position andthe exhaust valve opens. This completes the operating cycle.

FIG. 15, a-h, presents the sequence of operations for a cool pistonregenerated engine operating on a two stroke cycle. Only the majorcomponents of this engine are shown. These are: the cylinder (1), thecylinder head (2), the piston (3), the intake port (6), the exhaust port(7), the regenerator (8), the regenerator drive rod (9), and the fuelinjector (10). Either or both of the intake and exhaust ports could bereplaced by valves, which would provide greater flexibility in theopening and closing times. The intake port is located slightly lowerthan the exhaust port so that the exhaust port is uncovered by thepiston prior to the intake port.

The sequence starts with the piston near its BDC position, theregenerator adjacent to the cylinder head, and the intake and exhaustports having just been opened (a). While the piston is at and near toits BDC position, fresh working fluid flows in through the intake portand forces spent working fluid out of the exhaust port. The piston thenbegins to move toward the cylinder head (b) covering the intake port andthen the exhaust port (c). The piston then moves to its TDC position,thereby performing a compression stroke and compressing the workingfluid trapped in the cylinder. Just before the completion of thiscompression stroke the regenerator begins to move away from the cylinderhead and toward the piston in its regenerative heating stroke (d). Asthe piston completes its compression stroke and begins its expansionstroke, fuel is injected into the space between the moving regeneratorand the cylinder head (e). As the fuel reacts with the working fluid andthe piston continues its expansion stroke, the regenerator continues tomove toward the piston. The motion and timing of this portion of theregenerative heating stroke are such that the flow through theregenerator is always toward the hot volume, where the fuel is reacting.During the first quarter of the piston's expansion stroke, theregenerator overtakes the piston and continues to move with it (g). Whenthe piston's expansion stroke is about half complete, the regeneratorreverses its direction and begins to move back toward the cylinder headin its regenerative cooling stroke (h). The regenerator completes thiscooling stroke as the piston approaches its BDC position. This completesthe operating cycle.

FIG. 16 presents the sequence of operations for a hot piston regeneratedengine operating on a two stroke cycle. The engine is identical to thatshown in FIG. 15 and has the same components.

The operating cycle begins with the piston at its BDC position, theregenerator adjacent to the piston, and the intake and exhaust portshaving just been opened (a). The piston and regenerator then movetogether toward the cylinder head, thereby covering the intake port andsubsequently the exhaust port (b-c). The piston then moves to its TDCposition (d), thereby performing the remainder of its compressionstroke. The regenerator remains adjacent to the piston. Just before thecompletion of this compression stroke the regenerator begins to moveaway from the piston and toward the cylinder head in its regenerativeheating stroke (e). As the piston completes its compression stroke andbegins its expansion stroke, fuel is injected into the space between themoving regenerator and the piston (f). As the fuel reacts with theworking fluid and the piston continues its expansion stroke, theregenerator continues to move toward the cylinder head. The motion andtiming of the regenerative heating stroke are such that the flow throughthe regenerator is always toward the hot volume, where the fuel isreacting. During the first quarter of the piston's expansion stroke, theregenerator reaches the cylinder head and remains adjacent to it. Whenthe piston's expansion stroke is about half complete, the regeneratorbegins to move back toward the piston in its regenerative cooling stroke(g). The regenerator completes this cooling stroke, reaching andremaining adjacent to the piston, as the piston approaches its BDCposition (h). This completes the operating cycle.

The regenerator provides an excellent catalyst support structure. It hasa large surface area and nearly all of the working fluid passes throughit twice during each cycle. It is at a high temperature which is oftendesirable for many chemical reactions. Catalysts are utilized to promotethe destruction of pollutants, such as oxides of nitrogen, and they arealso used to promote or initiate combustion. For example, catalystscould be placed on and in a regenerator to increase the reactivity ofthe fluid passing through it. If the fluid contained fuel, then thisincrease in reactivity could serve to ignite it. Otherwise, thisincrease in reactivity would cause preliminary chemical reactions thatenhance the ignition or reaction of the working fluid as it flows intothe hot volume. Catalysts could also be used to promote the reaction ofany particulate matter (e.g. soot) or other incompletely reacted fuelproducts that pass into the regenerator. In the presence of appropriatecatalysts, the carbon soot and any hydrocarbons trapped in theregenerator could serve as reducing agents for oxides of nitrogen.

Catalysts can be deposited upon the internal surfaces of all or aportion of the regenerator. Catalysts that function best at hightemperatures can be placed within the hotter regenerator sections, whilethose that require lower temperatures can be placed within the coolersections. The wide temperature gradient across the regenerator providesa selection of temperature regimes. Regenerators with catalytic coatingscan be used to promote or retard combustion (or both, depending upon thelocal and current temperature) and/or to promote the destruction ofpollutants (e.g. oxides of nitrogen, unburnt hydrocarbons, and soot).

The regenerator of a regenerated engine is a porous material throughwhich the working fluid will flow and exchange energy with theregenerator--that is, it is an alternating flow heat exchanger. Thesmall openings within the regenerator through which the working fluidflows can be of uniform shape and size (as in a honeycomb or a screen)or they can be of a variety of shapes and sizes (as in ceramic foamsmade from reticulated plastic foam). If the openings are of nonuniformsize or shape, they are generally assigned some average value. Forexample, with reticulated plastic foams and their derivatives, whichhave pores of nonuniform size, the foam pore size is generally reportedin terms of a number of pores per inch--an average value. While all thepores are not of this size, an 80 pore per inch foam will have smallerflow passages on average, then a 40 pore per inch foam. Thus whether theregenerator material has flow passages of uniform size and shape ornonuniform size and shape, each such material can be assigned an averageor representative value for the size of its flow passages. In thefollowing discussion, all reference to flow passage sizes refers to thematerial's average flow passage size.

When designing a regenerator the first thought is to use a singlematerial for the regenerator heat transfer and storage medium. Theprevious inventions of Ferrenberg and that of Millman are of this type.However, there are many reasons to use different regenerator materialsas shown in the following examples.

As with all heat exchangers, it is advantageous to have a high surfacearea to promote rapid heat transfer and large flow passages to minimizepressure drop. Unfortunately, large flow passages generally result inlower surface areas. In the regions of the regenerator where thetemperatures are lower, the density of the gas flowing through will belower. This means that the velocity of the gas in these cooler regionswill be lower and the pressure drop across these regions will be muchlower. This phenomena can be used to construct a regenerator thatmaximizes heat transfer surface area while minimizing pressure drop. Ifthe regenerator is constructed with smaller size flow passages in itscooler regions, the pressure drop can be minimized while the surfacearea is maximized.

Another advantage of using materials having flow passages of differentaverage size is that particles (e.g. soot) are more readily trapped inregions of smaller flow passages. By placing the smaller flow passagematerial in a region with beneficial thermal conditions it is possibleto capture and contain these particles in that region. The temperaturesin these regions may be more conducive to the combustion of theseparticles or for the use of catalysts on the regenerator's internalsurfaces that promote desirable chemical reactions with the capturedparticles.

As an example, FIG. 17a presents a regenerator design based upon thisprinciple. The upper region of the regenerator (30) lies on the hot sideof the regenerator. This upper region is composed of a material withsmaller flow passages (for example, 100 pore per inch silicon nitridefoam). The remainder of the regenerator (31) is composed of a materialwith larger flow passages (for example, 70 pore per inch silicon carbidefoam). Most combustion generated soot particles will be captured in thesmaller flow passages of the hot side region where the temperatures arehighest. This will promote the oxidation of this soot, thereby reducingsoot emissions from the engine.

Smaller passages often provide greater structural strength in theregenerator material. These regions of smaller flow passages can be soarranged as to improve the overall stiffness and strength of theregenerator. For example, the regenerator can be constructed withnarrow, radial arms of smaller flow passage foam extending outward fromthe center of the regenerator.

Finally, the flow through the regenerator during the regenerativeheating stroke has a beneficial effect on the combustion. This effect isdue to the turbulence that the regenerator will produce in thecombustion region just before and during the combustion. The regeneratorcan also be designed to provide substantial swirl to the working fluidentering the combustion region. This is done by varying the flow passagesizes in different sectors of the regenerator. The intent is to producea greater flow through the regenerator in some areas and a lesser flowin others. This will result in large scale turbulence and swirl in thecombustion region.

FIG. 17b demonstrates how this concept can be applied in practice. Theleft half of the regenerator (30) is constructed of a material havingsmaller flow passages. The right side (31) is constructed of a materialwith larger flow passages. During the regenerative heating stroke, theflow through the regenerator will be greater on the right side than onthe left side, resulting in a swirling motion in the hot volume.

A new class of materials has been discovered that offers great promisefor use in the regenerator. These materials are referred to as "ceramicfoams". They are made from, and have the general shape of, common,reticulated (open cell) plastic (e.g. polyurethane) foams. The plasticfoam is converted to a carbon foam and then coated with a ceramic,refractory, or other material. The carbon foam can then be removed,leaving only the ceramic. The coating process may be accomplished inseveral ways, including ceramic slurry deposition and chemical vapordeposition or infiltration. The end result is a ceramic foam--a skeletalstructure consisting of a large number of nonuniform, unaligned,interconnected cells or pores separated by ligaments of solid material.These ceramic foams can be formed from many different materialsincluding common and refractory metals, silicon carbide, siliconnitride, and ceramics. Some minimal structure may be required to providesupport for the ceramic foam, especially where it is attached to thedrive rod.

Regenerated engines require a driving means to move the regenerator atthe appropriate times in the cycles. Some potential drive mechanismsare:

1. The regenerator may be moved by one or more drive rods passingthrough the cylinder head. The movement of these rods can be controlledby cams, chains (e.g. a timing chain), gears, linkages, hydraulicactuators, electrical solenoids, combinations of these, or other commonmeans.

2. The regenerator may be moved by one or more drive rods passingthrough the piston. The movement of these rods can be controlled bycams, chains, gears, linkages, hydraulic actuators, electricalsolenoids, combinations of these, or other common means. Any of themeans employed in Stirling engines to move a displacer (in some Stirlingengines the displacer is also a regenerator), such as the crank devicereferred to as a "rhombic drive", can be employed to move regeneratordrive rods.

3. The regenerator may be moved by a cylindrical annular sleeve passingbetween the piston and the cylinder wall. The movement of the sleeve canbe controlled by cams, chains, gears, linkages, hydraulic actuators,electrical solenoids, combinations of these, or other common means.

4. The regenerator may be moved, fully or in part, by a device hereafterreferred to as a pneumatic regenerator lifter and described in thefollowing.

A pneumatic regenerator lifter makes use of the pressures within thecylinder and the dynamic forces acting on the regenerator to provide allor part of the force required to move and position the regenerator. In acold piston regenerated engine the regenerator remains adjacent to thecylinder head except for one movement down to the piston (theregenerative heating stroke) and a return movement (the regenerativecooling stroke). Similarly, the regenerator in a hot piston engineremains adjacent to the piston except for one movement to the cylinderhead and a return. The pneumatic lifter is based upon the fact that thecylinder pressure is highest whenever the regenerator is required toaccomplish these movements.

There are a large number of ways by which this concept of a pneumaticregenerator lifter can be applied. However, all of these are based uponthe principles presented here. The basic features of one embodiment ofthe pneumatic lifter are presented in FIG. 18. This Figure depicts theuse of a pneumatic lifter in a cool piston regenerated engine. It can besimilarly applied to all other regenerated engines by application of thebasic principles presented here. The engine depicted in FIG. 18 could bea two or a four stroke engine, such as the ones shown in FIGS. 1 and 3.It could operate with any of the cool piston operating sequencespresented herein, such as FIGS. 4,6,7,13, and 15. Only the compressionand expansion stroke are shown. Also, only components that are requiredto demonstrate the operating sequence of this embodiment of thepneumatic lifter are shown.

Like all the other regenerated engines, this engine has a piston (3)(sometimes referred to here as the large or primary piston) within acylinder (1) that is closed at one end by a cylinder head (2). Thispiston contains a small internal cylinder (40) that is open to thecrankcase on one end (41) and open to the interior of the cylinder onthe other end (42). The diameter of this internal cylinder isexaggerated in FIG. 18 for clarity. Within this small internal cylinderis a small or secondary piston (43) which is attached to the regeneratordrive rod (9) that passes into the small cylinder through the opening(42) in the piston face. A spring (44) is attached at one end to thesmall piston, and at the other end to the upper part of the smallcylinder. This spring provides just enough upward force on the smallpiston to maintain the regenerator at the top of the cylinder when thelarge piston is at its BDC position. The small piston, the drive rod,and the regenerator (8) are moved by the combined forces of the springand the pressure difference between the cylinder and the crankcase.Although it is anticipated that a number of springs and spring-likedevices will be required or can be advantageously employed to controlthe motion of the regenerator, the following discussion of the pneumaticlifter concept assumes only a single spring. This is done for thepurpose of clarity and brevity in this disclosure of the pneumaticlifter concept.

The spring (44) is attached to the upper surface of the internalcylinder (40) and to the upper surface of the small piston (43). At thestart of the compression stroke (a) (in either a two or a four strokeengine) the large piston is at its bottom dead center position. At thattime the spring is near its relaxed position, but with just enoughtension to keep the regenerator at the top of the cylinder. During thecompression process (a to b) the large piston rises causing the springto be stretched and holding the regenerator firmly against the cylinderhead. As the compression occurs, the cylinder pressure rises. As thelarge piston approaches its top dead center position, the pressurebecomes great enough to overcome the spring tension and forces theinternal piston down. Since the small piston is rigidly attached to theregenerator, the regenerator moves toward the primary piston (b to c).As the regenerator moves the working fluid is forced through it andheated, thereby further increasing the cylinder pressure. The smallpiston is thus forced to its lowest position within the primary pistonand the regenerator is held against, or very close to, the large piston.As the regenerator is moving toward the piston, fuel is injected and thecombustion heat released further increases the pressure. Duringapproximately the first half of the expansion stroke (c to d), thepressure remains high enough to keep the regenerator adjacent to thelarge piston. At this point the tension forces in the spring exceed thereduced pressure force and the internal piston and the regenerator areforced upward. As the regenerator moves up (e), the thermal energy inthe gas is transferred to the regenerator. This further reduces thecylinder pressure thus causing the regenerator to rise still higheruntil it reaches the top of the cylinder.

There are a variety of ways by which this pneumatic lifter can be usedto move the regenerator. The use of a spring below the small piston andundergoing compression rather than tension also appears advantageous. Inorder to optimize the regenerator motion, and to prevent rapidaccelerations and stopping of the regenerator, it may be desirableand/or necessary to have several springs of different sizes and designsacting on the internal piston or the regenerator drive rod. Hydraulicand pneumatic springs can also be used. The diameter of the internalcylinder and the small piston can also be used to control the size ofthe pressure force and hence, regenerator motion. Also, the openingbetween the large cylinder and the small cylinder can be designed toslowly "bleed" pressure into the small cylinder for slower regeneratorresponse. Similarly the opening between the small cylinder and thecrankcase can be used as an orifice to retard the downward motion of thesmall piston.

The volume of the small cylinder should be as small as possible so asnot to significantly affect the compression ratio or serve as a heatsink for the working fluid. Since the movement of the regenerator onlyrequires the overcoming of the aerodynamic forces (pressure drop throughthe regenerator) and the regenerator's inertia, and since these forcesshould be relatively small, a very small internal cylinder should beadequate. In fact, recognizing that the drive rod itself is acted uponby the cylinder pressure, it may be possible to use the regeneratordrive rod itself as the small piston. This approach is preferred as itminimizes the gas volume in the small cylinder.

The pneumatic lifter concept can also be applied with the small cylinderand piston located in the cylinder head. The regenerator drive rod wouldthen extend through the head and attach to the upper side of theregenerator.

FIG. 20 presents another embodiment of the pneumatic lifter thatdemonstrates some of the features just discussed. In this case it isapplied to a hot piston engine that has a regenerator drive rod passingthrough the cylinder head. This engine could be any of the hot pistondesigns previously presented, such as that of FIG. 2. It could operateon a two or a four stroke cycle. Only the main components of the engineare shown: the cylinder (1), the cylinder head (2), the piston (3), theregenerator (8) and the regenerator drive rod (9). The cylinder head hasa hole through it (50) that accommodates the regenerator drive rod. Thishole has sealing devices, such as common O-rings or metal piston ringsto prevent leakage from the cylinder. The rod is acted upon by a spring(52) pressing against a small flange (51) attached to the drive rod.This spring is always compressed, that is, it exerts a downward force onthe rod at all regenerator positions. Thus, the spring always strives tokeep the regenerator adjacent to the piston and the pressure within thecylinder opposes the spring force.

During the final portion of the compression stroke and the first half ofthe expansion stroke, the pressure force within the cylinder becomesgreat enough to overcome the spring force. This forces the regeneratorupward against the cylinder head. Note that with this version of thepneumatic regenerator lifter, the small internal piston has beenreplaced by the regenerator drive rod. If greater pressure force isneeded, a small piston attached to the drive rod and moving in a smallcylinder within the main cylinder head (2) can be added.

The use of the pneumatic lifter in a regenerated engine offers severalimportant advantages. First, it makes the engine more compact, since noexternal mechanism for moving the regenerator is required. Second ituses the pressure forces directly rather than taking power from thecrankshaft to move the regenerator. And perhaps most importantly, itprovides a means to move and position the regenerator from either thecylinder head or the piston. This is useful because it will allow allseals and moving parts to be removed from the hot volume.

The pneumatic regenerator lifter can be applied in any type ofregenerated engine that employs a movable regenerator. This wouldinclude both two and four stroke engines; hot and cool pistonregenerated engines; engines that employ direct or indirect fuelinjection or utilize a premixed fuel and air mixture (a carburetor orinjection in the intake manifold); and supercharged, turbocharged, ornaturally aspirated engines.

As the load on conventional diesel engines is decreased, the air to fuelratio is increased and the peak temperatures decline. If this sameapproach is applied to regenerated engines operating at very low loadsthe temperatures will drop so low that engine efficiency will bereduced. In order to prevent the temperature from dropping too low, itmay be advantageous to reduce engine power by decreasing the flow of airthrough the engine and maintaining lower air to fuel ratios, as iscommonly done with gasoline engines. This can be done by reducing (i.e.throttling) the flow of working fluid into the cylinder by the use of avalve or other flow restriction device in the intake manifold.

Such a throttling device is shown in FIG. 20. This is the same engine aswas presented in FIG. 1. More of the intake manifold (13) is shown.Within that intake manifold is a device (50) that partially blocks theflow of air to the cylinder when moved to some position and provideslessor blockage in other positions. This approach is applicable to anyregenerated engine.

An alternative approach for reducing the flow of working fluid into thecylinder at lighter loads is to close the intake valve early during theintake stroke or to close it later in the compression stroke. This wouldrequire an engine with variable valve timing, a technology that is justnow being put into practice.

As the load or speed of the regenerated engine changes, it isthermodynamically advantageous to change the regenerator's motion--thatis, the timing of the regenerative heating and cooling strokes and theirspeed. This can be done using techniques currently in use or beingdeveloped that provide variable valve timing. One such method currentlyunder development is often referred to as an "electronic cam". It useselectromechanical devices to provide the opening and closing motion ofthe valves. A larger version of this type of device could bebeneficially applied to provide variable regenerator motion. Otherdevices currently being developed or used to provide variable valvetiming could similarly be adapted to control the motion of theregenerator. Finally, other common mechanisms employing chains, gears,cams, levers, and other common components can be used to providevariable regenerator motion.

Because of the regenerative heating that occurs prior to fuel injection,the temperatures of the working fluid at the start of combustion in aregenerated engine are higher than they would be in any conventionalengine operating at the same air to fuel ratio. As a result, the peakworking fluid temperatures in the cylinder that occur during combustionare also much higher. These high temperatures require the use of hightemperature, low conductivity materials and coatings on many internalsurfaces in order to protect the metallic structure and components ofthe engine. These thermal barriers reduce the greater heat lossassociated with the higher engine operating temperatures. These thermalbarriers consist of ceramic coatings or monolithic plates or sheets orother structures made of materials that can withstand high temperaturesand have low thermal conductivity. In addition, high temperaturelubricants, piston rings and fuel injectors may be required. As a resultof the use of these thermal barriers and other high temperaturecomponents, the regenerated engine may not require a water coolingsystem (radiator, water pump, et. al.). Depending upon the level ofinsulation provided, the regenerated engine may be sufficiently cooledby the surrounding air and by the oil. Thus, superior regeneratedengines will employ these thermal barriers and will be Low HeatRejection (LHR) regenerated engines. Much of this thermal barrier andLHR technology has been developed under programs in the Dept. of Energyand the Army.

All descriptions of the regenerated engine presented herein weredescriptions of a single working unit of a regenerated engine. A singleworking unit consists of a single cylinder containing a piston. Mostregenerated engines would be made up of a number of these individualworking units. Generally, some or all of the intake and exhaustmanifolds would be connected together and all of the pistons would beconnected to a single crankshaft.

All regenerated engines must have means for the introduction of freshworking fluid and the expulsion of spent working fluid from the coldvolume of the cylinder. These intake and exhaust means may consist ofvalves of any type, including: poppet valves (as shown in the Figures),rotary valves, slide valves, butterfly valves, ball valves, sleevevalves, or any other type of valve that can provide suitable flow andoperating characteristics. These valves can be flush with the cylinderwall when closed, as is shown in FIG. 1, or they can be located someshort distance from the cylinder and be connected to the cylinder viaports or passages. These intake and exhaust means can also be simpleopenings (often called ports) that are located in the cylinder wall andare opened and closed by being covered and uncovered by the piston, asis commonly done in small two stroke engines. However these intake andexhaust means are configured and placed, they must permit the flow ofworking fluid into and out of the cold volume. When any of these intakeor exhaust means are "open", this indicates that they are so positionedor arranged that working fluid can pass through them between thecylinder and the appropriate manifold. It should be understood thatalthough only single intake or exhaust means were presented in thisdisclosure, in every case, multiple means could be applied. For example,there could be two or more intake valves in FIG. 1.

Valves cannot be opened or closed instantaneously. Thus some time mustbe allotted for their opening and closing. Also, at higher enginespeeds, the flows into or out of the cylinder will be slower, on a flowrate per crank angle basis, then they are at lower speeds. Inconventional gasoline and diesel engines maximum volumetric efficiencyis attained at higher speeds by opening valves early and closing themlate. The valve timing is set for one engine speed (or sometimes twowith variable valve timing) and operation at other speeds must beperformed with less than optimum timing. This same approach isapplicable to regenerated engines. Therefore, the valve opening andclosing times presented herein should be viewed with an understandingthat there may be considerable variation in them. When intake or exhaustmeans are referred to as being "substantially" open or closed this meansthat they are fully open or nearly fully open or they are nearly closedor closed, respectively. It is understood that there may be some timeprior to, or after, this time that the intake or exhaust means will becompleting the opening or closing.

Throughout this disclosure, the regenerator has been viewed as a thin,cylindrical disc. For an engine with a flat-faced piston and a flatcylinder head, this is the ideal shape, as it allows all of the internalvolume of the cylinder to be swept by the regenerator. However, it isoften advantageous to use pistons and heads that have surfaces that arenot flat. For example, cylinder heads often have sloped surfaces toprovide more room for valves. In order for the regenerator to fullysweep through the entire internal cylinder volume, the regeneratorshould be constructed so as to closely match the contours of the pistonand the cylinder head. That is, the top of the regenerator should fitagainst the cylinder head with only minimal gaps and the bottom shouldfit against the piston face with only minimal gaps.

In all of the processes disclosed herein it must be understood thatspecial operating conditions and other considerations may dictate minorchanges in the timing of the events of these processes. Also, it isobvious that, based upon the teachings presented herein, manymodifications and variations of this invention are possible. Therefore,it should be understood that, within the scope of the appended claims,the invention may be practiced otherwise than as specifically describedherein.

It should be understood that "means to introduce fuel" includes allmeans by which fuel can enter the hot volume. This includes (1) directinjection into the hot volume, (2) injection into the cold volume andsubsequent passage of the fuel through the regenerator, and (3) theintroduction of the fuel into the working fluid prior to the workingfluid's entry into the cylinder and the subsequent passage of the fuelthrough the regenerator and into the hot volume.

For some fuels with large ignition delays (e.g. lighter hydrocarbonssuch as propane and natural gas) and for some operating conditions (e.g.starting, idling, and lightly loaded), it may be necessary to provide anadditional ignition source such as a spark plug or a glow plug.

Finally, all regenerated engines can have boosted intake pressures or benaturally aspirated. Also, all the regenerated engines presented hereinemploy a regenerator that does not have sealing devices to preventleakage between the hot and cold volumes through the flow path betweenthe regenerator and the cylinder wall. It is believed that no suchsealing devices are required as long as a reasonably close fit betweenthe regenerator and the cylinder wall is maintained. However, it mayprove to be advantageous to provide some sealing means around theperiphery of the regenerator. Such sealing means could be conventionalpiston rings, labyrinth seals or other common types.

Obviously, many modifications and variations of the present inventionare possible in light of the above teachings. It is, therefore, to beunderstood that within the scope of appended claims, the invention maybe practiced otherwise than as specifically described.

What is claimed and desired to be secured by Letters Patent of theUnited States is:
 1. An internal combustion, reciprocating, regeneratedengine having a number of similar working units, each working unitcomprising:a) a cylinder, closed at one end by a cylinder head andcontaining a movable piston which moves in a reciprocating manner and isconnected to a power output shaft; b) intake means for permitting theflow of fresh working fluid into said cylinder during a predeterminedtime during each operating cycle; c) exhaust means to permit the flow ofexhaust fluid from said cylinder during a second predetermined timeduring each operating cycle; d) a thermal regenerator located withinsaid cylinder and between said piston and said cylinder head, saidregenerator being an alternating flow heat exchanger which can be movedbetween said piston and said cylinder head;the movement of saidregenerator including a regenerative heating stroke which begins duringthe last quarter of said piston's compression stroke and ends afterexpansion has begun and during the first quarter of said piston'sexpansion stroke, said regenerative heating stroke also being ofsufficient speed and timing so as to maintain, to the greatest extentpossible, a flow of working fluid out of said regenerator, through saidregenerator's hot surface and into the hot volume, throughout saidregenerative heating stroke; e) means for moving said regenerator duringadditional predetermined times during the engine's operating cycle; andf) means for introducing fuel into said cylinder.
 2. The internalcombustion engine of claim 1 wherein the opening and closing of saidintake means is so arranged and timed that the degree of compressionwhich said working fluid experiences is less than the degree ofexpansion which said working fluid experiences.
 3. The internalcombustion engine of claim 2 wherein each working unit operates on a twostroke cycle, said intake means not allowing said working fluid to entersaid cylinder until after the start of said piston's compression stroke,thereby providing an effective compression ratio that is less than theeffective expansion ratio.
 4. The internal combustion engine of claim 2wherein each working unit operates on a four stroke cycle, and in whichsaid intake means are substantially closed before said piston reachesits bottom dead center position at the end of its intake stroke.
 5. Theinternal combustion engine of claim 2 wherein each working unit operateson a four stroke cycle, and in which said intake means remain openduring a substantial portion of said piston's compression stroke,thereby allowing some of said working fluid introduced into saidcylinder during the intake process to be forced back out of saidcylinder through said intake means.
 6. A process for operating theengine of claim 2 in a two stroke cycle, said engine having intake andexhaust means that communicate with the internal cylinder volume locatedbetween said piston and said regenerator, said process comprising thefollowing steps:a) opening said exhaust means when said piston isapproaching its bottom dead center position, said intake means areclosed, and said regenerator is adjacent to said cylinder head; b)moving said piston toward said cylinder head; c) opening said intakemeans, thereby allowing fresh, pressurized working fluid to enter saidcylinder and to push out some of the remaining exhaust fluid throughsaid exhaust means; d) closing said exhaust means; e) continuing themovement of said piston toward said cylinder head while working fluidcontinues to enter said cylinder; f) closing said intake means; g)continuing said piston's movement toward said cylinder head, therebyperforming a compression stroke whereby the working fluid trapped withinthe cylinder is compressed; h) moving said regenerator away from itsposition adjacent to said cylinder head and toward said piston as saidpiston approaches its top dead center position near the conclusion ofsaid compression stroke; i) introducing fuel into the space between saidmoving regenerator and said cylinder head while said piston completesits compression stroke and begins to move away from said cylinder headin its expansion stroke; j) continuing the movement of said regeneratortoward said piston while said piston continues its movement away fromsaid cylinder head, said regenerator overtaking and being adjacent tosaid piston before the completion of the first quarter of said expansionstroke; k) moving said regenerator and piston together at the same speedaway from said cylinder head; l) slowing the movement of saidregenerator during the middle portion of said piston's expansion stroke,thereby increasing the distance between said regenerator and saidpiston, and beginning to move said regenerator toward said cylinderhead; and m) continuing the movement of said piston toward its bottomdead center position while said regenerator moves to a position adjacentto said cylinder head.
 7. A process for operating the engine of claim 2in a two stroke cycle, said engine having intake and exhaust means thatcommunicate with the internal cylinder volume located between saidcylinder head and said regenerator, said process comprising thefollowing steps:a) opening said exhaust means when said piston isapproaching its bottom dead center position, said intake means areclosed, and said regenerator is adjacent to said piston; b) moving saidpiston and regenerator together toward said cylinder head; c) openingsaid intake means, thereby allowing fresh, pressurized working fluid toenter the cylinder and to push out some of the remaining exhaust fluidthrough said exhaust means; d) closing said exhaust means; e) continuingthe movement of said piston and regenerator toward said cylinder headwhile working fluid continues to enter said cylinder; f) closing saidintake means; g) continuing the movement of said piston and regeneratortogether and toward said cylinder head, thereby performing a compressionstroke whereby said working fluid trapped in said cylinder iscompressed; h) moving said regenerator away from its position adjacentto said piston and toward said cylinder head as said piston approachesits top dead center position near the conclusion of said compressionstroke; i) injecting fuel into the space between said moving regeneratorand said piston as said piston completes its compression stroke andbegins to move away from said cylinder head in its expansion stroke; j)moving said regenerator to a position adjacent to said cylinder headwhile said piston continues its expansion stroke, said regeneratormovement being completed during the first quarter of said expansionstroke; l) moving said regenerator from its position adjacent to saidcylinder head and to a position adjacent to said piston, said movementbeginning during the middle portion of said piston's expansion strokeand ending as said piston approaches its bottom dead center position. 8.A process for operating the engine of claim 2 in a four stroke cycle,said engine having intake and exhaust means that communicate with theinternal cylinder volume located between said piston and saidregenerator, said process comprising the following steps:a) opening saidexhaust means when said piston is near its bottom dead center position,said intake means are closed, and said regenerator is adjacent to saidcylinder head; b) moving said piston to its top dead center positionnear to said cylinder head, thereby performing an exhaust stroke wherebyspent working fluid is expelled from said cylinder; c) opening saidintake means as said piston approaches the end of said exhaust stroke;d) moving said piston from its top dead center position to its bottomdead center position, thereby performing an intake stroke and drawingfresh working fluid into said cylinder; e) closing said exhaust meansduring the early part of said intake stroke; f) closing said intakemeans during said intake stroke; g) moving said piston toward saidcylinder head, thereby performing a compression stroke whereby saidworking fluid that is trapped within said cylinder is compressed; h)moving said regenerator away from its position adjacent to said cylinderhead and toward said piston as said piston approaches its top deadcenter position near the conclusion of said piston's expansion stroke;i) introducing fuel into the space between said moving regenerator andsaid cylinder head while said piston completes said compression strokeand begins to move away from said cylinder head in its expansion stroke;j) continuing the movement of said regenerator toward said piston whilesaid piston continues its movement away from said cylinder head, saidregenerator overtaking and being close to said piston before thecompletion of the first quarter of said expansion stroke; k) moving saidregenerator and piston at the same speed away from said cylinder head;l) slowing the movement of said regenerator during the middle portion ofsaid piston's expansion stroke, thereby increasing the distance betweensaid regenerator and said piston, and beginning to move said regeneratortoward said cylinder head; and m) continuing the movement of said pistontoward its bottom dead center position while said regenerator moves to aposition adjacent to said cylinder head.
 9. A process for operating theengine of claim 2 in a four stroke cycle, said engine having intake andexhaust means that communicate with the internal cylinder volume locatedbetween said piston and said regenerator, said process comprising thefollowing steps:a) opening said exhaust means when said piston is nearits bottom dead center position, said intake means are closed, and saidregenerator is adjacent to said cylinder head; b) moving said piston toits top dead center position near to said cylinder head, therebyperforming an exhaust stroke whereby spent working fluid is expelledfrom said cylinder; c) opening said intake means as said pistonapproaches the end of its exhaust stroke; d) moving said piston from itstop dead center position to its bottom dead center position, therebyperforming an intake stroke and drawing fresh working fluid into saidcylinder; e) closing said exhaust means during the early part of saidintake stroke; f) moving said piston toward said cylinder head whilemaintaining said intake means open until a portion of said working fluidis expelled through said intake means and out of said cylinder; g)closing said intake means; h) moving said piston to its top dead centerposition close to said cylinder head, thereby performing a compressionstroke whereby said working fluid remaining within said cylinder iscompressed; i) moving said regenerator away from its position adjacentto said cylinder head and toward said piston as said piston approachesits top dead center position near the completion of said compressionstroke; j) introducing fuel into the space between said movingregenerator and said cylinder head while said piston completes itscompression stroke and begins to move away from said cylinder head inits expansion stroke; k) continuing the movement of said regeneratortoward said piston while said piston continues its movement away fromsaid cylinder head, said regenerator overtaking and being close to saidpiston before the completion of the first quarter of said expansionstroke; l) moving said regenerator and piston at the same speed awayfrom said cylinder head; m) slowing the movement of said regeneratorduring the middle portion of said piston's expansion stroke, therebyincreasing the distance between said regenerator and said piston, andbeginning to move said regenerator toward said cylinder head; and n)continuing the movement of said piston toward its bottom dead centerposition while said regenerator moves to a position adjacent to saidcylinder head.
 10. A process for operating the engine of claim 2 in afour stroke cycle, said engine having intake and exhaust means thatcommunicate with the internal cylinder volume located between saidcylinder head and said regenerator, said process comprising thefollowing steps:a) opening said exhaust means when said piston is nearits bottom dead center position, said intake means are closed, and saidregenerator is adjacent to said piston; b) moving said piston andregenerator together toward said cylinder head, thereby performing anexhaust stroke whereby spent working fluid is expelled from thecylinder; c) opening said intake means as said piston and regeneratorapproach the end of said exhaust stroke; d) moving said piston from itstop dead center position to its bottom dead center position, keepingsaid regenerator close to said piston, and thereby performing an intakestroke whereby fresh working fluid is introduced into said cylinder; e)closing said exhaust means during the early part of said intake stroke;f) closing said intake means during said intake stroke; g) moving saidpiston and regenerator together and toward said cylinder head, therebyperforming a compression stroke whereby the air trapped in the cylinderis compressed; h) moving said regenerator away from its positionadjacent to said piston and toward said cylinder head as said pistonapproaches its top dead center position near the conclusion of saidcompression stroke; i) injecting fuel into the space between said movingregenerator and said piston as said piston completes its compressionstroke and begins to move away from said cylinder head in said piston'sexpansion stroke; j) moving said regenerator to a position adjacent tosaid cylinder head while said piston continues its expansion stroke,said regenerator movement being completed during the first quarter ofsaid expansion stroke; and k) moving said regenerator from its positionadjacent to said cylinder head and to a position adjacent to saidpiston, said movement beginning during the middle portion of saidpiston's expansion stroke and ending as said piston approaches itsbottom dead center position.
 11. A process for operating the engine ofclaim 2 in a four stroke cycle, said engine having intake and exhaustmeans that communicate with the internal cylinder volume located betweensaid cylinder head and said regenerator; said process comprising thefollowing steps:a) opening said exhaust means when said piston is nearits bottom dead center position, said intake means are closed, and saidregenerator is adjacent to said piston; b) moving said piston andregenerator together toward said cylinder head, thereby performing anexhaust stroke whereby spent working fluid is expelled from saidcylinder; c) opening said intake means as said piston and regeneratorapproach the end of said exhaust stroke; d) moving said piston from itstop dead center position to its bottom dead center position, keepingsaid regenerator close to said piston, and thereby performing an intakestroke whereby fresh working fluid is introduced into said cylinder; e)closing said exhaust means during the early part of said intake stroke;f) moving said piston and regenerator together and toward said cylinderhead while maintaining said intake means open until a portion of saidworking fluid is expelled through said intake means and out of saidcylinder; g) closing said intake means; h) moving said piston andregenerator together toward said cylinder head, thereby performing acompression stroke whereby the working fluid trapped in said cylinder iscompressed; i) moving said regenerator away from its position adjacentto said piston and toward said cylinder head as said piston approachesits top dead center position near the conclusion of said compressionstroke; j) injecting fuel into the space between said moving regeneratorand said piston as said piston completes its compression stroke andbegins to move away from said cylinder head in said piston's expansionstroke; k) moving said regenerator to a position adjacent to saidcylinder head while said piston continues its expansion stroke, saidregenerator movement being completed during the first quarter of saidexpansion stroke; and l) moving said regenerator from its positionadjacent to said cylinder head and to a position adjacent to saidpiston, said movement beginning during the middle portion of saidpiston's expansion stroke and ending as said piston approaches itsbottom dead center position.
 12. The internal combustion engine of claim1 in which said fuel is introduced into the hot volume, where combustionoccurs, by passing through the hot surface of said regenerator.
 13. Theinternal combustion engine of claim 1 in which said fuel introductionmeans are placed so as to provide direct introduction of fuel into thespace within said cylinder on the cold side of said regenerator.
 14. Theinternal combustion engine of claim 1 in which said intake and exhaustmeans communicate with the cylinder volume located between said pistonand said regenerator, and in which said fuel is introduced into theworking fluid entering said cylinder prior to the entry of said workingfluid into said cylinder, said fuel being transported into said cylinderby and with said working fluid.
 15. The internal combustion engine ofclaim 1 in which said intake and exhaust means communicate with thecylinder volume located between said regenerator and said cylinder head,and in which said regenerator movement includes a regenerative coolingstroke, whereby said regenerator is moved from a position close to saidcylinder head to a position close to said piston during said piston'sexpansion stroke, and in which said fuel is introduced into the workingfluid entering said cylinder prior to the entry of said working fluidinto said cylinder, said fuel being transported into said cylinder byand with said working fluid.
 16. The internal combustion engine of claim1 in which at least a portion of said fresh working fluid that enterssaid cylinder during each operating cycle, enters through passages insaid means for moving said regenerator.
 17. The internal combustionengine of claim 1 in which at least a portion of said spent workingfluid that leaves said cylinder during each operating cycle, leavesthrough passages in said means for moving said regenerator.
 18. Theinternal combustion engine of claim 1 in which means are provided forreducing the amount of the working fluid that enters the cylinder duringeach operating cycle, thereby reducing engine power while maintaininghigh efficiency.
 19. The internal combustion engine of claim 1 in whichsaid intake means comprise one or more valves that open and close one ormore passages in the cylinder wall, said valves being substantiallyflush mounted in said cylinder wall when closed.
 20. The internalcombustion engine of claim 1 in which said exhaust means comprise one ormore valves that open and close one or more passages in the cylinderwall, said valves being substantially flush mounted in said cylinderwall when closed.
 21. The internal combustion engine of claim 1 in whichthe entire internal volume of said cylinder is so arranged as to allowthe regenerator to pass through all of said internal cylinder volume,with the exception of small clearance regions.
 22. A process foroperating the internal combustion engine of claim 1 in a two strokecycle, said engine having intake and exhaust means that communicate withthe internal cylinder volume located between said piston and saidregenerator, said process comprising the following steps:a) opening saidexhaust means when said piston is approaching its bottom dead centerposition, said intake means are closed, and said regenerator is adjacentto said cylinder head; b) opening said intake means; c) moving saidpiston to its bottom dead center position and initiating movement ofsaid piston toward said cylinder head; d) closing said exhaust means; e)closing said intake means; f) continuing to move said piston toward saidcylinder head, thereby performing a compression stroke whereby theworking fluid trapped within said cylinder is compressed; g) moving saidregenerator away from its position adjacent to said cylinder head andtoward said piston as said piston completes said compression stroke andbegins to move away from said cylinder head in said piston's expansionstroke,this separate movement of said regenerator beginning during thelast quarter of said piston's compression stroke and ending during thefirst quarter of said piston's subsequent expansion stroke when saidregenerator reaches said piston, said regenerator's movement also beingof sufficient speed and timing as to maintain, to the greatest extentpossible, a flow of working fluid out of said regenerator, through saidregenerator hot surface and into the hot volume, throughout saidregenerator's movement; h) introducing fuel into the space between saidmoving regenerator and said cylinder head while said piston completesits compression stroke and begins to move away from said cylinder headin its expansion stroke; i) moving said regenerator and piston together,at the same speed, away from said cylinder head; j) slowing the movementof said regenerator during the middle portion of said piston's expansionstroke, thereby increasing the distance between said regenerator andsaid piston, and beginning to move said regenerator toward said cylinderhead; and k) continuing the movement of said piston toward its bottomdead center position while said regenerator moves to a position adjacentto said cylinder head.
 23. A process for operating the internalcombustion engine of claim 1 in a two stroke cycle, said engine havingintake and exhaust means that communicate with the internal cylindervolume located between said regenerator and said cylinder head, saidprocess comprising the following steps:a) opening said exhaust meanswhen said piston is approaching its bottom dead center position, saidintake means are closed, and said regenerator is adjacent to saidpiston; b) opening said intake means; c) moving said piston to itsbottom dead center position and initiating movement of said pistontoward said cylinder head, while maintaining said regenerator adjacentto said piston; d) closing said intake means; e) closing said exhaustmeans; f) continuing the movement of said piston and regeneratortogether and toward said cylinder head, thereby performing a compressionstroke whereby the air trapped in the cylinder is compressed; g) movingsaid regenerator away from its position adjacent to said piston andtoward said cylinder head as said piston completes said compressionstroke and begins to move away from said cylinder head in said piston'sexpansion stroke,this separate movement of said regenerator beginningduring the last quarter of said piston's compression stroke and endingduring the first quarter of said piston's subsequent expansion strokewhen said regenerator reaches said cylinder head, said regeneratormovement also being of sufficient speed and timing as to maintain, tothe greatest extent possible, a flow of working fluid out of saidregenerator, through said regenerator's hot surface and into the hotvolume, throughout said regenerator's movement; h) injecting fuel intothe space between said moving regenerator and said piston as said pistoncompletes its compression stroke and begins to move away from saidcylinder head in said piston's expansion stroke; and i) moving saidregenerator from its position adjacent to said cylinder head and to aposition adjacent to said piston, said movement beginning during themiddle portion of said piston's expansion stroke and ending as saidpiston approaches its bottom dead center position near the conclusion ofsaid piston's expansion stroke.
 24. The internal combustion engine ofclaim 1 in which said regenerator contains catalytic materials on someportion of said regenerator's surfaces that are exposed to said workingfluid, said catalytic materials serving to increase the reactivity ofthe working fluid passing through it.
 25. The internal combustion engineof claim 1 in which said regenerator contains catalytic materials onsaid regenerator's surfaces that promote chemical reactions that reducepollutants in the spent working fluid passing through said regenerator.26. The internal combustion engine of claim 1 in which said regeneratorcontains catalytic materials on some portion of said regenerator'ssurfaces that are exposed to said working fluid, said catalyticmaterials increasing the reactivity of chemical reactions that utilizesoot and hydrocarbons trapped in the regenerator to destroy oxides ofnitrogen.
 27. The internal combustion engine of claim 1 in which saidregenerator has internal flow passages that are of different averagesize in different portions of said regenerator.
 28. The internalcombustion engine of claim 1 in which at least one secondary piston isconnected to said regenerator, said secondary piston being acted upon bythe pressure in said cylinder so as to provide at least a portion of theforce required to place said regenerator at predetermined positionswithin said cylinder at predetermined times during the operating cycle.29. The internal combustion engine of claim 1 in which said means formoving said regenerator are adjustable so as to provide variations inthe cycle to cycle movement of said regenerator.